Coal

Coal is a black colored fuel item that can be obtained in a variety of ways.

Mining
Coal can be found naturally underground in the form of coal ore, which drops coal when mined with most pickaxes. It can also be obtained by using a molten axe on a log. Mining quicksand with a stone shovel has a chance of dropping coal. Nether coal ore also drops coal when mined.

Crafting
Coal can be made from block of coal and vice versa.

Incinerators
Incinerators will occasionally produce coal alongside the ash.

Nether fortress loot
Coal can rarely be found in nether fortress chests.

Crafting
Coal can be used to craft a variety of useful items.

Brewing
Coal can be placed into a cauldron.

Fuel
Coal can be used to smelt 8 items in a furnace, or 16 items in a forge.