Skills are very important. They make up what your character can do when rolling the dice. How you allocate them during character creation will affect what you can and cannot do while on mission.
Physical Skills
Agility:
With the amount of stuff that collapses, gets thrown, is fired or is otherwise directed at the average Poolboy during their tenure, the ability to move quickly and efficiently around, over, under and away from obstacles and attacks is always very useful. Agility can be rolled for such feats as dodging falling rubble, stepping carefully on dangerous ground, as well as offensively for tripping or stumbling opponents. This skill is also used to accurately fling objects in a precise way, as when trying to throw an object through a small gap.
Agility can also be used to avoid melee attacks, and, at higher levels, skilled Agents may even be able to dodge certain ranged and thrown attacks, such as from a bow.
Strength:
Agility is great for getting places, but when it comes to moving things around, carrying heavy loads and going the extra mile, nothing beats Strength. The stronger an Agent is, the more force and effort they can apply to physical tasks such as climbing, tackling opponents, or breaking open locked doors. This skill is also used to chuck something around with brute force if no real degree of extreme accuracy is needed, like when throwing a grenade.
Perception:
Even in the midst of an alien dimension, your senses are your best weapon - the smallest things your character sees, smells, hears, tastes or feels could be the key to getting out alive. This is generally rolled when a GM has something that may or may not be noticed by a character.
Social Skills:
Characters can use social skills to talk someone out of a rash course of action, intimidate them into doing their will, barter for a better reward or simply bullshit their way out of a bad situation. There are multiple sub-skills under this banner: Persuasion, Intimidation, and Bluff are the three foremost, but any number of other possibilities exist (consult a GM with regards to alternate social fields).
In the case of social skills being used against other PCs, the player of the character being targeted determines the effectiveness of the argument, regardless of the success of the roll; social skills cannot be used to 'hijack' other players' characters.
Persuasion:
Characters who are Persuasive are able to influence the beliefs and attitudes of those around them, bringing them more in line with their own. This skill could be used to talk down the entity throwing lightning at you, convince the judge that you're innocent of all those horrible things you're accused of, or to rally fellow team members in the face of otherwise certain defeat. Persuasion rolls are opposed by Mental Defense.
Intimidation:
A character with points in this skill has a higher chance of invoking fear or alarm in others. It could be used as a means of deterring attackers, or to frighten a sapient vending machine into giving you your change. Intimidation rolls are opposed by Mental Defense.
Bluff:
Agents with high Bluff scores are adept at lying, conniving and generally being untruthful. On mission, this could mean your character convincing a murderous cultist that they are interested in converting to his religion, or confusing a guard into letting them pass by without identification. Bluff rolls are opposed by Perception.
Technical Skills
The specialized skills are those which require specific training to use, skills which could not be simply "picked up" in day-to-day life. Rolls involving specialized skills may require characters to possess a certain level of skill to attempt (this level is set at GM discretion) and characters with 0 in a specialty skill cannot attempt under any circumstances
Medical:
Whether it's offering a bandaid, or removing a six foot long steel spike from parts better not mentioned in polite company, those endowed with the healing touch are always a welcome sight at the Red Pool. Points in Medical allow a character to attempt to repair some of the physical injuries that naturally accumulate during forays into the depths of SCP-354, getting Agents back on their feet and into the fray. If your character is Medical staff, they are required to have at least 4 points in the skill.
Sneak:
Slippery, crafty and downright spooky. The defining trait of Espionage Agents, points in Sneak (as the name implies) will affect how stealthily you move, and make it hard for you to be spotted when you don't want to be, meaning it's perfect for getting out of being filled with holes by that sentry. Since the ability to remain unseen gives rise to great temptations, a higher Sneak skill means that you'll be able to pickpocket and lockpick even more easily than before.
An important note is that Sneak is the only Specialty skill you do not need points in to roll.
Engineering:
Mechanical, like Science and Academics, covers a wide variety of disciplines; from swinging a wrench to designing buildings. Nevertheless, all Foundation Engineers have that basic engineering mindset, no matter what their speciality; though it's probably not a good idea to get the architect to fix the plumbing. Engineering rolls may deal with repairing and operating machinery, building objects, and any other physically based technology rolls. If you need it built, repaired or destroyed, call the engineers.
Hacking:
In a world ever more dependent on technology, hackers, crackers and general tech-heads are a valuable commodity. There's all sort of weird, wonderful and possibly lethal tech to encounter in the Red Pool, so Agents with points in Electronics can be extremely useful. Rolls using this skill will reflect the character's proficiency with computers, including using, hacking, repairing and understanding complex programming in all manner of things - from door controls to massive killer robots.
Science:
The very foundation of the Foundation, Science covers a wide range of disciplines - everything from Geology to Theoretical Physics and back again. If your character is in Research then this skill will be heavily used, and they'll require at least 4 points so as not to feel inadequate. This can be rolled for all manner of science-related activities - for example, mixing some chemicals to make a powerful acid, setting up a boulder to roll at the right angle down a hill to crush a tank or just trying to work out what species something is.
Academics:
A skill well-fitting for high-Persuasion agents of Espionage, Academics is the 'Arts' equivalent of a Science roll. A character possessing a high academia skill is well acquainted with areas of study outside of study such as law, literature, culture, and language. Analyzing language patterns, determining cultural customs, and decoding books and puzzles are some of the skills Academics users may come to rely on. Additionally, any character with one or more points in Academics may be declared bilingual, while trilingualism or polyglotism are possible only with GM approval.
Survival:
The many and varied environments of the Pool are not always the friendliest places to explore. When all your equipment has been lost and you're standing buck naked in an alien forest without a friend in the world, or when you need to follow that creature you saw run off with your radio, it's good to know how to survive and thrive in the wild. This skill may be used in place of an academics roll for identification of survival-based objects, such as edible plants or suitable sites to make camp. May also be used for tracking, finding shelter and several other creative uses that are up to the player.
Offensive Skills
Ranged Combat:
When facing the latest unspeakable horror vomited forth by the Red Pool, many an agent has taken great comfort in the knowledge that large calibre weaponry is close at hand. Well, at least until it turns out that whatever it is is completely intangible. Regardless, ranged weapons like guns, bazookas, bows or any other form of projectile firing apparatus are pretty much the default weapon among Foundation employees.
Melee Combat:
When all else fails, and the enemy is closing in, it's time to fight with anything close at hand - including your hands. Melee weapons can be anything capable of making a close range attack - from fists and feet to knives and clubs. A pretty basic, all-rounder skill for combat.
Defensive Skills
Physical Defense:
No matter how agile or sneaky you are, it's likely that you're going to take a hit from something at some point. Whether it's fist, a shockwave or a sentient, swearing cannon ball, there's a lot of stuff that starts flying when the proverbial hits the fan. Counteracting these is your character's PDef - how well do they take a hit? This is rolled every time a physical attack is used against them that they don't dodge.
Mental Defense:
The Red Pool is filled with horrible things, quite a few of which are far beyond human comprehension and most of which aren't good to be around. Unsurprisingly, encountering these creatures and events takes a toll on even the most prepared mind. Exactly how badly your character is affected by psychic, memetic, or just plain mind-fucking attacks is decided by their MDef. Based on the roll a GM decides what kind of effects occur to the character - for instance whether they end up losing a mind point. This can also be rolled against persuasion from another PC, however the outcome of the roll is entirely up to player discretion.
Body:
An indicator of overall physical well-being. At zero Body, the character is either unconscious or incapable of action due to pain or grievous wounds. Body damage, if unhealed during the course of the run, will be automatically healed at its conclusion.
Mind:
An indicator of your overall mental health. At zero Mind, the character is either brain-dead or has suffered a complete psychotic breakdown. Mind damage cannot be healed in the usual way; instead it restores at the rate of one point every three weeks, unless stated otherwise by a GM.