Skills
A skill is any kind of knowledge or ability that you can get better at through practice and training. Athletics, perception, computers, and history are examples of skills. Having a skill makes tasks relating to that skill easier.
Your core character starts with two skills. The skills you can choose from depend on the genre of the game the GM is running (such as sci-fi, fantasy, or postapocalypse).
You have the option of starting with a third skill, but in exchange you have to pick a meaningful skill that you're bad at (called an inability). Having an inability in a skill makes tasks relating to that skill harder. For example, you could choose climbing as your third skill, but you'd have to pick another skill (like perception or stealth) to be bad at.
When you pick a skill for your inability, it has to be something meaningful that could significantly impact your character from time to time, such as climbing, perception, or persuasion, not a skill like farming or philosophy.