Strength is a measure of your raw physical power. It affects how much you can carry, the power of all melee attacks, and your effectiveness with many heavy weapons.

A high Perception grants a bonus to the Explosives, Lockpick and Energy Weapons skills, and determines when red compass markings appear (which indicate threats).

Endurance is a measure of your overall physical fitness. A high Endurance gives bonuses to health, environmental resistances, and the Survival and Unarmed skills.

Having a high Charisma will improve people's disposition toward you, and give bonuses to both the Barter and Speech skills.

Intelligence affects the Science, Repair and Medicine skills. The higher your Intelligence, the more Skill Points you'll be able to distribute when you level up.

Agility affects your Guns and Sneak skills, and the number of Action Points available for V.A.T.S.

Raising your Luck will raise all of your skills a little. Having a high Luck will also improve your critical chance with all weapons.