It is obtained with a wooden pickaxe or better. It drops a small amount of experience, and tends to be found in large veins.
Coal is used in alternative torch recipes by using Natura sticks instead of vanilla Minecraft stick. There is also a Stone Rod variant added by Tinkers' Construct used for torches. It is also used in the crafting of the Fire Medallion.
Coal, due to its lack of rarity and it's strength, is one of the most efficient smelting fuels. It will sustain a furnace long enough to smelt eight items.