Although there are many players who train Woodcutting purely for experience, using chopped logs for Fletching is the primary focus and use of the skill. Players with a higher Woodcutting level can chop down new types of trees and cut down trees quicker. Another benefit to high Woodcutting is that with higher levels, players can use better axes to chop trees down. Players with high enough Attack levels can equip the axes that match the respective metals, but you don't need to equip an axe to use it to cut down a tree. It can be in your inventory.
To begin Woodcutting, go to your magic spell book and click on the Skill Teleport. Head over to where it says Woodcutting & Firemaking, and choose Woodcutting. As you travel to this place, you arrive in the front yard of a church surrounded by many trees. To begin you'll need hatchet, which can be purchased from the Woodcutter. Use your Hatchet on a Tree to cut Logs. Depending on your level, you will gain access to new trees, and new logs for other skills.
In order to cut logs, you must have at least one type of Hatchet which you have the level required to use. These can be bought from the Woodcutter at ::WC.