Redstone is an element that is used as an ingredient for most mechanical creations in Minecraft, and it's required in some way to get most mechanisms to operate.
Redstone may be dropped when a block of Redstone Ore is destroyed with an iron or diamondpickaxe It is also dropped by Witches (which is why it is renewable), and occurs in block form in Jungle Temples and Woodland Mansions. Cleric Villagers will also sell up to 4 redstone dust for Emeralds. It can also appear in Dungeon, Woodland Mansion, StrongholdChests, and Abandoned MineshaftChest Minecarts. This dust can be placed on the ground to make redstone wire. Redstone dust can be crafted into a Redstone Torch, although a redstone torch is not as efficient as a regular torch as it does not give off as much light, it can be used in many redstone mechanisms. Redstone dust can also be crafted into block form for both storage and mechanical purposes. Redstone dust also can be used in traps or mechanisms involving redstone circuits. Redstone dust can also be crafted into Redstone Repeaters that can be used for extension and other mechanical purposes. When redstone interacts with any liquid, it will be destroyed. Redstone dust can only be placed on solid blocks, excluding Glowstone and top placed Slabs of any kind. When redstone dust gets ignited, it will last 15 blocks before going to its off state. This can be prevented by placing a repeater and continuing the redstone circuit however will make the output 1-4 ticks longer. A Redstone Comparator (see page for details) creates an instant redstone signal when placed in a line (all facing the same way) unlike repeaters (listed above). The toggle switch must be off in order for this to happen. Redstone dust is also used as an ingredient in potions to make the effects last longer.
In older versions of Minecraft Pocket Edition, redstone dust didn't drop from its ore no matter what pickaxe is used. Redstone dust also did not have much of a function until the implementation of some utility items that can be used from redstone.