Health

The health and damage system in minecraft is based on a simple heart system. Each heart contains halves. All player characters and hostile mobs have 10 hearts at full health, and 0 at death. Pigs, sheep, and cows all have 5 hearts, whilst chickens have 2 hearts. Players and NPCs can do damage by hitting each other with items at close range. The large majority of items only do ½ a heart of damage. Certain items can be crafted for the explicit purpose of dealing more damage. Swords are the main and simplest item to use and make. Swords still require melee range, but deal significantly more damage per hit.
 * Wooden Sword: 2 hearts/hit
 * Stone Sword: 3 hearts/hit
 * Iron Sword: 4 hearts/hit
 * Diamond Sword: 5 hearts/hit

Besides swords, there are several other unique items that can be used to deal extra damage. Arrows for example, that must be shot using right click with a bow, are the only ranged weapon in the game. Flint&steel is an item that allows the player to light a block on fire, which causes all players and mobs that walk over the block to be caught on fire. Players and mobs that are caught on fire by the flint&steel stay on fire for 15 hits, or until they touch water. Like Flint and Steel, a bucket of lava also catches enemies on fire. Lastly, TNT is currently the only explosive weapon in Minecraft and is consequentially quite hard to obtain.
 * Arrows: 2 hearts/hit
 * Flint&steel: ½ heart/hit, 1 heart/hit if the player/mob is standing on the flaming block
 * Bucket of Lava: 5 hearts/hit while player/mob is in lava ½ heart/hit from afterburn.
 * TNT: 12 hearts/hit (point blank), equivalent to a Creeper explosion on hard difficulty.

Mob's Damage
Unlike player character's damage, the damage mobs do is effected by the difficulty the player is on.

Easy

Zombie: 1½ hearts/hit

Spider: ½ heart/hit

Skeleton: 1 heart/hit

Creeper: 5½ hearts/hit (point blank)

Normal

Zombie: 2½ hearts/hit

Spider: 1 heart/hit

Skeleton: 2 hearts/hit

Creeper: 8 hearts/hit (point blank)

Hard

Zombie: 3½ hearts/hit

Spider: 1½ hearts/hit

Skeleton: 3 hearts/hit

Creeper: 10½ hearts/hit (point blank)

Natural Damage
Besides mobs, players can take damage from several other events in Minecraft. This does not commonly happen to mobs because they automatically float upwards. falls on him. Approximately ½ heart damage/sec. if the player/mob stands next to it. stay on fire even if they exit the lava. If players do not have a water source available they will die quickly.
 * Fall Damage: ½ heart if falling from 4 blocks ½ heart more for every extra block.
 * Drowning: Once your air runs out underwater, you will take approximately ½ heart damage/sec.
 * Suffocation: Occurs when the player/mob is somehow inside of solid blocks, most commonly if sand or gravel
 * Cacti: Touching a cacti will cause a player/mob to take ½ heart damage, and rapidly continue taking damage
 * Lava: By far the most dangerous natural occurrence, players/mobs will take damage extremely fast, and

Trivia
very fast damage, and slows enemies in their tracks. The only downside is that a large amount of the time the mob's drop will be disintegrated in the lava.
 * A bucket of lava is arguably the most efficient weapon in the game, as it doesn't use up durability, does