Item

Items are objects which only exist within the player's inventory and hands - which means, they cannot be placed in the game world. Some items simply place blocks or entities into the game world when used. They are thus an item when in the inventory and a block when placed. Some examples of objects which exhibit these properties are item frames, which turn into an entity when placed, and beds, which turn into a group of blocks when placed. When equipped, items (and blocks) briefly display their names above the HUD.

Items use item IDs while blocks use block IDs.

Materials
Are used for a lot of different purposes, mainly creating other blocks or items.
 * Mob drops are used for consuming, cooking, creating other blocks or items, teleporting, playing music, and as ammo, blocks, weapons, armor, and tools. These are obtained by picking up the item that drops after a mob dies. Some mobs will not drop (certain) items when not registered as killed by a player (spiders with spider eyes, and blaze with blaze rods). Adult chickens drop (lay) eggs every 5 to 20 minutes.
 * Minerals are used for tools, fuel for a furnace, creating other blocks or items, trading, dyes, and work in redstone contraptions. These are obtained by picking up the item that drops after mining an ore with a pickaxe of the right material, or taking the item that gets created after smelting an ore.
 * Plants (in non-block form, examples: seeds, and sugarcane (item version)) are used for creating block-type plants when placed on farmland, dirt, sand, and the side of logs, so that they can grow, and give themselfs or other items in the game when fully grown and broken, and be manufactured or consumed. These are obtained by picking up the item that drops after breaking a block-type version of the non-block plant in the world, or are found in reward chests.
 * Dyes are used to color certain blocks, items, or sheep to get their respective color of wool when shearing them. Primary dyes are obtained similar to mob drops, minerals and plants. Examples of these are ink sacs, which are mob drops from squids, lapis lazuli, which is a mineral, and rose reds, which are the output of putting red flower-plants in a crafting grid. Secondary and tertiary dyes are obtained by combining two primary or secondary dyes together in a crafting grid, examples: lime, cyan, purple, gray, and more. Some dyes can be a secondary or tertiary dye, but also be crafted by putting a flower-plant in a crafting grid.
 * Crafting Ingredients are ingredients that have no specific category and no other non-decoration purpose than to create other blocks or items by crafting or smelting, examples: flint, bowls, sticks, paper, clay items, brick items, netherbrick items, and nether quartz items. These are obtained by a lot of different causes.
 * Brewing Ingredients are ingredients that are necessary to create potions, examples are blaze powder, ghast tears, glistering melons, and more. The main ingredients for potions are water bottles and nether wart, except for weakness potions, which you can create without nether wart. To make a splash potion, which you can throw instead of drink, you need to add gunpowder to a potion. To get better potions effects, you need to either add glowstone dust to make it a tier two, or redstone to extend its duration. These two cannot be legitimately combined together on one potion.
 * Enchanting Ingredients are ingredients that are only used for enchanting related things, examples: enchanted books and bottle o' enchanting (experience bottles). These are obtained by enchanting, or trading with a villager.

Food
Is used to be eaten by the player to get (back) hunger points and saturation, or eaten by wolves or dogs to give them health, or to make dogs and pigs breed. Some food items will give status (potion) effects to the player.
 * Normal Food, such as apples, bread, melons, pumpkin pie, steak and more, will only give back hunger points and saturation, without any other effect.
 * Good Food, such as golden apples can give the player (several) (good) status effects, such as regeneration, absorption, fire resistance and resistance.
 * Bad Food, such as raw chicken, rotten flesh, spider eyes, and pufferfish, can give the player (several) bad status effects, such as hunger, poison, and nausea. If you are about to starve and only have this food, you can drink milk afterwards to clear all their (bad) status effects.

Tools
Are used for a variety of purposes, mainly to help the player do things, and be coordinated.
 * Axes allow the player to break wood-type blocks faster than mining by hand. They can be crafted from wood, cobblestone, iron, gold and diamond.
 * Shovels allow the player to break sand-type blocks faster than mining by hand. They can be crafted from wood, cobblestone, iron, gold and diamond.
 * Pickaxes allow the player to break stone-type blocks faster than mining by hand, and are required in different types of materials in order to make resources drop from specific stone-type blocks. They can be crafted from wood, cobblestone, iron, gold and diamond.
 * Hoes allow the player to till dirt, allowing them to plant crops, examples: seeds, carrots, and pumpkin seeds. They can be crafted from wood, stone, iron, gold and diamond.
 * Buckets allow the player to transport liquids such as water and lava, and get milk by right-clicking a cow or mooshroom.
 * Shears allow the player to make sheep drop wool, mooshrooms drop red mushrooms, cobwebs drop string, with a silk touch enchantment the actual cobweb itself, and make varieties of tall grass, leaves, vines and dead bushes drop themselves. They can also be used to break and collect tripwire without activating connected redstone dust.
 * Flint And Steel allows the player to set most blocks on fire for varying periods of time. Some blocks will be burned (destroyed without an item dropping) by this process. They also allow the player to light nether portals on fire, so that nether portal blocks are formed inside. A fire charge has the same (and more) effects, but will be used up after one use, and is a ranged projectile opposed to a tool.
 * Fishing Rods allow the player to go fishing to catch several types of fish, treasure, and trash, as well as pull mobs or players closer.
 * Informative Tools assist the player in coordinating in the world.
 * Maps are, when looked at, making blocks render in itself that are shown as colored pixels, respective to their rendered block.
 * Compasses are always pointing exactly with their red arrow at the player's original spawn point. (For players with Pre-release Alpha and Beta worlds, may have had this point "shift" as spawn points were coded in the region files, not derived from the seed.)
 * Clocks are showing the player what time it is in the over-world. When located in the nether, or the end they will rapidly spin.

Weapons
Are mostly used to kill mobs and players faster strategically.
 * Swords are used to kill mobs and players faster, to block attacks, which reduces most types of damage by half, or to break blocks a little faster.
 * Bows (with Arrows) are used to kill mobs or players from a distance.
 * Snowballs are used (in this context) to knock players or mobs back, giving you time to run. They only deal damage to Enderdragons and Blazes.
 * Eggs are used (in this context) to knock players or mobs back, giving you time to run. They do not deal damage to any entities.
 * Fishing Rods are used (in this context) to knock players or mobs back, giving you time to run. They do not deal damage to any entities. They can also pull mobs and players towards you, giving people using ranged combat no advantage.
 * Enderpearls are used (in this context) to teleport away from or into combat. When used, the player will take 2.5 hearts of damage but feather falling and protection enchantments will reduce this.
 * Flint and Steel, Fire Charges and Lava Buckets are used (in this context) to light players on fire.
 * Empty Buckets are used (in this context) to steal a player's lava or water, giving them a disadvantage.

Armor
Are used to reduce damage from mobs, players, lava, and explosions. Armor enchants increase this reduction.
 * Helmets, Chestplates, Leggings, and Boots are a full set of mob/player armor that reduces damage for them. Zombies and skeletons can rarely drop this when they spawned wearing it. When a player throws armor (or any item) at a zombie or skeleton, and they pick it up, they will drop it upon any kind of death.
 * Horse Armor is used to protect a horse from damage similar to player armor, but can only be worn by a tamed horse.
 * Water Buckets are used (in this context) to put a player on fire quickly out.
 * Milk is used to erase all (good and bad) status (potion) effects.

Transportation
Are used allow to move players, mobs or items over land or water with relative speed and ease.
 * Minecarts are used to travel much faster across rails, they are also used to store and pick up items or work in and activate redstone circuitry. When placed down they are an entity.
 * Boats are used to travel much faster across water (for example over oceans, rivers and lakes). When placed down they are an entity.
 * Saddles and Carrots on Sticks are used, and needed, to travel on pigs and/or horses.
 * Leads are used to right-click on most passive mobs, so they will follow you. Mobs will get pulled closer when they're too far away from the player, but, if they can't get to the player, and the distance is too far, the lead will break and drop on the place where the mob is.
 * Wheat, Carrots and varieties of Seeds are used to make most passive mobs follow you, when it's held. In Multiplayer when other players are too close by, they will not, or stop, following the player.

Potions
Are brewed, drinkable or throwable items that confer specific effects. Producing them requires resources from the nether, and sometimes from the overworld. The main ingredients are water bottles, and nether wart, which are used to create every potion in the game, with the exception of a weakness potion because you don't need netherwart for it.
 * Gunpowder is used to make a splash potion, which you can throw to other mobs and players, instead of consuming it yourself.
 * Glowstone Dust is used to get a tier two potion.
 * Redstone is used to extend the duration of a potion.
 * Glowstone dust and redstone cannot be legitimately combined together on one potion.

Music Discs
Are musical items textured similar to real life discs, that when put in a jukebox will create music. They are obtained by letting a creeper die by an arrow shot from a skeleton, or disc 'Cat' and '13' are found in dungeon reward chests. There are twelve different discs in the game.

Eggs and Spawn Eggs

 * Eggs are used to spawn 1 or 4 baby chickens.
 * Spawn Eggs are re-textured eggs with dots, they are colored similar to their respective mob, and are used to spawn in most mobs in the game. These are obtainable only in creative mode. Right-clicking the same type of spawn egg on a mob that can have babies will spawn a baby mob on that place (wolves and all passive mobs can have babies like this, except squids and bats).

Decorational Items
Are used only for aesthetic purposes.
 * Fireworks are used for a beautiful scenery. They can be crafted in varieties of colors, shapes and sounds and when used will quickly fly up in the air and (visually and audibly) explode.
 * Book and Quills can be used to write down information or stories in a book.

Other
Are used for miscellaneous purposes.
 * Name Tags are used to name any kind of mob, and keep them from despawning. Naming a mob "Dinnerbone" or "Grumm" will turn them upside-down. Naming sheep "jeb_" will make its wool color fade into all 16 colors of dyed sheep, although this will not affect the drops of the sheep.