S.P.E.C.I.A.L. stands for Strength, Perception, Endurance, Charisma, Intelligence, Agility, and Luck. At the very beginning of the game, you'll formulate your S.P.E.C.I.A.L. statistics. It is important to choose what kinds of character that you want to be from the very beginning, because while you'll be given the ability during the game to put a point here and there to boost yourself, the large majority of S.P.E.C.I.A.L. points are chosen at the beginning of the game.
The maximum number of points that can be assigned to an attribute is 10. If you get a bonus to an attribute if it's already that high, there is no additional benefit beyond negating an existing penalty.
Strength[edit]
Strength is a measure of your raw physical power. It affects how much you can carry, and determines the effectiveness of all melee attacks.
Each point of strength adds 10 to your carry weight, and 2 to Melee Weapons Skill.
Perception[edit]
A high Perception grants a bonus to the Explosives, Lockpick and Energy Weapons skills, and determines when red compass markings appear (which indicate threats).
Each point adds 2 to Energy weapons, Explosives and Lockpick skills. It also provides a bonus to the range at which monsters appear as Green/Red bars on your compass.
Endurance[edit]
Endurance is a measure of your overall physical fitness. A high Endurance gives bonuses to health environmental resistances, and the Big Guns and Unarmed skills.
Each point adds 20 points to health, 2 to Big Guns and Unarmed skills. In addition, every point past the first provides 2% to Environmental Resistance.
Charisma[edit]
Having a high Charisma will improve people's disposition toward you, and give bonuses to both the Barter and Speech skills.
Each point adds 2 to Barter and Speech.
Intelligence[edit]
Intelligence affects the Science, Repair and Medicine skills. The higher you intelligence, the more Skill Points you'll be able to distribute when yo level up.
Each point adds 2 to Medicine, Repair and Science skills. You also gain 1 additional skill point per level.
Agility[edit]
Agility affects you Small Guns and Sneak skills, and the number of action Points available for V.A.T.S.
Each point adds 2 to Small guns and Sneak skills, and 2 Action Points.
Luck[edit]
Raising your Luck will raise all of your skills a little a high Luck will also improve you critical chance with all weapons.
A point in luck adds one to all skills; after that, every second point adds a point to each skill.