At the bottom of your screen, next to the Action Bar, is the Experience Bar.
You must fill your Experience Bar in order to Level Up, or advance to the next Level. At the bottom of your screen, next to the Action Bar, is the Experience Bar. Every time you defeat an enemy or finish a task, you get experience, which somewhat fills that meter. Your Level rises by one after the bar is fully filled. You will frequently receive a new Ability that you may add to your Action Bar and incorporate into the way you play your character. You will also typically receive additional Health and whatever Resource your Class requires. Keep in mind that certain Abilities are Passive, which means you don’t need to have them on your Action Bar for them to provide you bonuses automatically.