Woodcutting is,like its name, cutting wood. You can then Sell the wood, or make a fire from it.
To woodcut you need a hatchet. There is a free one in the stump on the farm on the east side of the river Lum. This is a bronze hatchet. Start by cutting a tree.
Here is the order of hatchets by level:
1 bronze hatchet
1 Iron hatchet
6 steel hatchet
6 black hatchet
21 Mithrill hatchet
31 Adamant Hatchet
41 Rune hatchet
As you advance in levels, you can chop down different kinds of trees.Here is the order:
1 normal tree
15 Oak tree
30 Willow tree
60 Yew
To get XP just chop trees!