it simply means "Im completely/totally OK with this" Cool, here refers to be ok with a certain situation. for example: If u come to my party and I feel ur a little bit uncomfortable, I may ask "Could I get u anything to drink?" and u could say "No thanks. I'm cool" it means no thanks, Im ok... "What do u say we goto Dalian this weekend?" "Im cool" (Its ok, I don't mind, Im ok with this, yeah sure)

cool = OK; fine;

"It's not a problem" is a similar meaning.

that is fine with me i like it or even i gree with what u already said