Sorry I know this is possibly in the wrong place, but does anyone know of a really good newbies guide to the BG series?
http://www.planetbaldursgate.com/bg/character/
Sadly this is the best guide I can find without photocopying the game manuals.
BG runs AD&D 2e ruleset. The abilities scores are rolled by making 3d6 (3 six sided dice) rolls to each score. All classes have prime abilities, for prime abilities it has to be at min of 9. That means if you have str of 9 you cannot be a fighter.
Str for fighter is somewhat different. Only a single class fighter can have str score beyond 18 at creation. It means once you've set str to 18, there are 5 more grades beyond that to represent how awesome you are, by rolling a d100. 18/00 (rolled a 100) is the best. You gain +3 attack/+6 damage for melee attack. Weapon specialization is also available only to fighters, be it single class or multiclass.
Each race has different restriction of class/multiclass. Each class may have different alignment restriction. Paladin can only be lawful good, ranger can only be good, druid must be partially neutral, bard cannot be lawful, monk must be lawful, etc. The alignment affects how hostile some NPCs are towards you.
The ruleset is pretty vast, would be best if you could ask more specifically.