Skills are the things that your character can do that you can’t just pick up and learn in a day or two. Skills are things like cooking food, fighting with a longsword, and enchanting magical items. They are things like playing chess, haggling, and lifting weights.
Skills are highly customizable and can be made to be either very general, such as taking a skill in all Athletic activities, or incredibly specific, like a Trivia skill focusing only on the anatomy of vampire bats. The more specific a skill is, the easier mastery will be to achieve.