Portal 2

[Tickle Me Emo]

is the co op random? or does it have 2 be with like your steam friends only?

also do you just re-do the existing missions in co op, or does co op have it's own set of maps and what not?

Co-op can be either with friends or random match. The co-op missions are unique from the single player (they're designed to be solved by 2 players rather than 1).