Wood aka Planks is an unnatural block that is made from trees. It is used in many recipes and it is very easy to obtain. Some people choose to make their homes out of wood to kind of give it a flair but it is very common for accidents with fire to happen and especially griefers. Griefers tend to target wood structures because they can easily be set on fire and when it is on fire it will spread.
Wood can also be used in a furnace as a heating element if you do not have any coal but it is not very effective. The axe is the best tool to chop wood.