These represent the learned skills of a character. They mostly refer to specific things which the character can or cannot do and some things must be learned as attempting them untrained will almost certainly result in failure.
In terms of the mechanics, skills are gained by spending XP in a similar way to abilities. However, they are cheaper than abilities. Again, this should be logical. For example, if a player has never been near a ship then they shouldn’t be able to learn how to pilot one (unless of course they’ve had some kind of expert instruction or learned through another means).
Skills are combined with abilities to give a total bonus. This is worked out as being 3/4s of ability + skill rank.