It works off base 10. 10 is the average for stats, though having higher or lower is quite common. A PCs ability stat (Strength, Dex, Stamina, Int...ect) is also the cap for their skills (A person with INT 10 cannot have the science skill at above 10).
Skills are divided up into Base Skills, Specialties, and Focuses. Base skills are the most broad examples in skills, while Specialties are more narrowly defined, and Focuses are directed at single examples. A Star Trek PC with the Base skill Scientific Knowledge might have the Specialties of Biology, Physics, and Engineering, and as the Focus of their biology, they might have Romulans. The number of skill points in a Focus can be no more than double that of the linked Specialty, which in turn can be no more than double its linked Base Skill. As mentioned, none of these can go over the Ability cap. However, each step towards focused adds another d10 to the roll.
How does this work, when it comes down to rolling? Glad you asked!
Say we have a security guard with
Guns: 3 -> Pistols: 5 -> Colt .45: 10
If the security guard were to shoot at a perp with, say, a shotgun, he would roll 1d10+10 for the dex, and 1d10+3 for the shotgun which adds up to 2d10+13 (a range of 15-33). Were he using a Beretta he picked up off the ground, he'd be better off, rolling 1d10+10 for dex, and 2d10+5 for pistols (a range of 18-45). If he actually used the gun he had focused on, his Colt .45, he'd be rolling 1d10+10 for dex, and 3d10+10 for his Focus (a range of 24-60).
Security guard shooting summary:
Any gun (15-33)
Colt .45 (24-60)
Compare this to a generalist who never focused
Any gun (22-42)
Note that the generalist is as proficient with most pistols as the Security Guard, and would be significantly better off than the security guard if he were asked to fire, say, an assault rifle.
Crits: To get a crit, you must hit a certain range of numbers on ALL the dice you roll. If you roll 2 dice, then the target number is 10. 3 dice, and the target is 9-10. 4 dice, and the target is 8-10.
Automatic Success: If your skill+attribute is greater than the Difficulty of the attempted action, you automatically succeed. This is the "Broad side of a barn" rule.
xp costs: Attributes cost 4xp per point. Base Skills cost 3 per point. Specialties cost 2 per point. Focuses cost 1 per point.
The above Security guard skills cost a total of 69xp. The generalist cost 70.
Anyone have any comments, suggestions, or requests?