You're advised to get them with karma, because it's a waste of a skill point. But basically, you can have the following on a skill:
- No specializations: You simply roll the normal dicepool
- One specialization: You add +2 dice when doing the specific action. For example, Athletics(Throwing) means you get a +2 when throwing, but not when climbing.
After chargen, you can also evolve to this:
- One Expertise: +3 on the action instead.
- One Expertise, a second Specialization: +3 on the expertise, +2 on the specialization, do not stack.
Sources:
- p92 "Show your talents" second paragraph
- p65 "Skill" third paragraph