Skills may be rolled vs. any [Stat]. All skills max out at 4 [CP] per +1 bonus.
Though skills *might* be used with any stat, most skills will have a really obvious core stat. Write down the sum of that stat and the skill on your character sheet. So you might have a character with DX 13, Math Ability and IQ 12:
* Guns (Pistol), DX/Easy, 4 pts=+2, 15+2: 17
* Mathematics, IQ/Hard, 2 pts=-1, 11+3: 14
Skills are similar to, but different from [Talents]
If your character is trying to learn new things like a normal person, use the SlowStudyRules. For heroic learning, look to a TrainingMontage.