Physical Skills
Physical skills involve doing stuff with your body. Since everyone has a body, the defaulting penalty for using physical skills untrained is zero. Without specialized training you can always still make a raw attribute test. A very strong person can grapple fairly effectively on that basis alone, an intuitive person can easily notice things, and so on and so forth.
Athletics
Athletics is the skill you use to run, jump, climb, swim, throw things, and generally do everything that you're vaguely expected to do in PE except sneak into the girl's locker room and get shamed by your peers. Most stunts are athletics based, and it can even be useful in attacking enemies in combat by dint of throwing things at specific targets.
Specializations: Climb, Jump, Run, Swim, Throwing
Combat
Combat is the training needed to fight. Usually other people. More than any other skill, people will ask to divide up Combat into smaller fragments. It is not immediately clear why, but we strongly suggest that you do not do this. While there are truly a vast array of differences between stabbing someone with a sword and shooting them with a gun - the simple fact that the combat simulationist player can name them all draws attention to how simply not that different they are. The basic truths of combat skill include making rapid life and death decisions while avoiding threats and putting the pointy end of your weapon into the other man. There's a world of differences from combat situation to combat situation, and that's why the skill goes all the way to six. But please remember that this is a game where flying a plane and managing a nuclear power plant can be the same skill (Operations).
Specializations: By weapon or martial style.
Drive
Drive allows people to drive culturally appropriate vehicles. For people in the west, that's mostly just cars. But for people in river areas or fishing communities, that's often small boats as well. Driving under safe conditions is such a banal and non-awesome thing, that characters do not need to actually make rolls to do it, so players may not even need the skill. But when it comes to dangerous driving conditions, car chases, or even just cutting commute times, rolls are generally required, and having the skill is helpful. This dichotomy is generally why in movies cars wipe out spectacularly the moment someone uses magic to create icy road conditions - a lot of people on the road are legitimately terrible drivers, and the moment things get harsh they become one of the 18,000 car accidents that happen every day in the US.
A character can drive a new non-standard type of vehicle for every rating point and specialization of the skill they have. Common choices are emergency vehicles, motor boats, construction equipment, armored vehicles, light aircraft, and oversized (semis and buses), but really players can pretty much go nuts. Any plane or ship which is piloted with dials and knobs rather than a wheel or stick is the domain of Operations rather than Drive.
Specializations: Bad Weather, Aggressive Driving, Cross Town Traffic, Navigation
Larceny
Characters skilled at Larceny are adept at working outside the law. It is a broad skill that covers lots of dubious activities, from identifying and bypassing security systems to picking other peoples' pockets. There is some overlap between Larceny and Rigging when dealing with locks. Locks are both geared puzzles and a basic hindrance to breaking into places. This is a good skill to have for security workers in addition to criminals. You gotta know your enemy if you're gonna win the war.
Specializations: Concealing Goods, Legerdemain, Lockpicking, Security Systems
Perception
Perception is the skill by which a character perceives the world around themselves. It is used to spot clues, notice subtle noises, and smell unfortunate smells. Characters with very low Perceptions are the characters who do not notice monsters sneaking up on them or have to have the meaning or import of subtle clues explained to them by other protagonists.
Specializations: By sense, Investigation, Noticing sneaking
Stealth
The Stealth skill is what one uses to avoid being noticed, either by moving quietly, becoming unseen against the background, or simply blending into the crowd. Whenever a character is being searched for, a Stealth check can be used to make that searching more difficult. Stealth involves using what is available, so there is almost no circumstance in which it cannot be used to at least postpone the moment that a character is noticed.
Specializations: Hiding, Innocuity, Shadowing, Sneaking
Survival
100% of the creatures alive today are the descendants of an unbroken line of ancestors who were all able to survive in their environment long enough to have had children that extends back to when single celled organisms had only two different nucleotides in their DNA. So persisting in the face of adversity is something that creatures have a birthright to. And yet, adversity has also kept up with the times. Survival is the skill of keeping up with the elements.
One can also make Survival checks to scavenge things of a more modern nature. A Survival check could be called for to loot useful things out of a junk yard or to track the layout of a sewer system.
Specializations: Tracking, Gathering, Shelter, by Environment.