I do play GURPS, and I'm not going to take the time to convert characters to other systems ... especially since I really don't know other systems (other than Fantasy Trip, a long out-of-print system that doesn't precisely have more players than GURPS).
But you should have a handle on what some of the numbers mean, so you have a good idea what these NPCs can do and how well they can do it.
(Caveat: the explanations are my own perception, usually. Not every GURPS GM shares my take.)
Stats: Stats are Strength, Intelligence, Dexterity and Health. There are also secondary stats such as Fatigue, Speed, Move, Perception, Will and Hit Points, which are all figured off of the main stats.
10 is the system default for "average" -- unless there's a racial modifier, every character starts with 10s in each of the main stats. Improving stats is expensive in GURPS, so stat numbers that a D&D player might perceive as only decent are in this system quite good. Almost all physical skills are bought off of DX, and almost all mental skills are bought off of IQ; in consequence, GURPS characters tend to be created with variations on 11-13-13-11 numbers, even after the major revision in 4th edition that jacked up the point cost on improving DX and IQ while leaving ST and HT alone.
7 is the lowest stat the system allows, and 8 is the lowest I allow: it's pretty much the lowest you can get and still be a viable adventurer. Still, a stat of 8 sucks, and over the years a number of players who blow through my warnings have traded out characters once they realize exactly how much it does suck.
12 is, IMHO, a pretty decent stat. 13 is very good indeed, and it's about what I encourage PCs to use for their go-to stat -- "prime requisite" in D&D terms. 14 is outstanding, something that a beginning PC might have as a "prime requisite" stat with some sacrifice; looking over my records, people manage with a single stat less than half of the time. More than that? In the 29 years I've been GMing GURPS, only eight characters have had a stat of 15 or more. All of them started before the 4th edition cost revision, and six of them played a race that gave a stat boost. One intrepid dwarf had ST 15/DX 15, and was otherwise a blithering idiot with just a half-dozen skills.
Skills: Basic premise -- in GURPS, beginning characters are competent.
This isn't D&D, where a character can only be reasonably expected
to succeed at a skill half of the time. A skill of 12 (which is okay at
best for a PC) has a 74% chance of success. A skill of 13 has 84%. A
skill of 15 has 95%. Penalties apply -- if you're trying to shoot someone in the countryside at midnight, from 30 yards away, you had damn well better not count on hitting him with that 14 roll -- but even so.
A level of 8-9 is better than the default level for not knowing a skill at all, but it's not very good; a good example is that Broadsword-8 means you've just finished boot camp, and you were clumsy to begin with. (The minimum DX you can have and have Broadsword-8 is 9.)
10-11 is okay. It'll do for routine, non-emergency, non-combat uses. Think of an apprentice in a craft, or someone of decent physical prowess just getting through basic weapon training.
12 is about the nominating level for "can make your living with this skill," and 13 is "... and you're actually good at it." 11-12 is where a newly-genned PC should have routine, secondary skills in the "It's Good To Have In The Party Someone Who Knows Something About History" camp.
14 is quite good, and 13-14 is about where a newly-genned PC should have important skills.
15 is where I place an expert, and a newbie with this for his or her go-to skill is doing okay. A newbie swordsman with DX 12, for instance, is putting a significant number of points to get Rapier skill this high.
16-17 are quite expert, and these are levels that newly genned PCs will only reach with serious sacrifice, and that I'll allow a newbie to take only if I'm in a pretty good mood.
18 is my nominating level for master, and few PCs ever push numbers this high or above.
21 is my nominating level for "best in the region," and I won't let PCs reach this without long training, serious sacrifice and some excellent explanations. (You don't get to be the best swordsman in the kingdom by going on adventures. You get to be the best swordsman in the kingdom by working out four hours a day, every day, with weapon masters in the salle.)
25 is my nominating level for "one of the best in the world." I've let exactly two PCs in my campaign's history reach this with a single skill apiece. The first was the best healer in my campaign's history, and the second is not merely the most powerful wizard (and highest point total character) in my campaign's history, she's legitimately one of the world's most powerful wizards.