Woodcutting is all about chopping down trees.
XP is gained whenever you break log blocks.
Tree Feller is an active ability, you can right-click while holding an ax to activate Tree Feller. This will cause the entire tree to break instantly, dropping all of its logs at once.
Leaf Blower is a passive ability that will cause leaf blocks to break instantly when hit with an axe. By default, this ability unlocks at level 100.
This passive ability gives you a chance to obtain an extra block for every log you chop.