Calculating Odds

[Nikita]

Ok, I've just started to learn about outs and figuring out pot odds--it has definitely improved my game and win percentage. But, I've noticed from some of your posts, that pot odds can be calculated pre-flop. I never considered doing this and actually (maybe I'm being dunce), I'm not sure how to do it. I understand how to do it, if I know how many outs I have, but pre-flop I don't have that information. Or do I? Are you just looking to get a pair? If you guys could clarify how calculating odds pre-flop works, I'd appreciate it. I hate calling all-ins and this will help me make better decisions on when to do so.