I'll give a brief guide to how you can calculate pot odds by yourself when you are playing poker. The idea is to know how many cards that are left in the card deck that will help you and how many cards there are left in total.

Let's say we're playing texas hold'em and have a deuce and a queen (We were in the big blind otherwise we would have folded those cards preflop). The flop comes 22K. We have three of a kind and drools a little when we think that we'll probably win this pot. But it would be even better if we could improve even more, wouldn't? What cards would help us then. A queen or a deuce would help us. There is 1 deuce left in the deck and three queens which makes four outs. There are five cards that you have seen (your own two hole cards and the three from the flop) so there are 52 - 5 = 47 unseen cards left. Thus the chance of us improving when the next card comes is 4 / 57 = 0.085. Almost 9% chance of improving then and this was what we were interested in.

If we were certain our opponent had 2 kings as his whole cards we would need to improve our hand to win. Let's say he makes a bet of 1 big blind and the pot is 20 big blinds including his bet. Then you must have pot odds better than 1 / 20 = 0.05 to call. How lucky! Our pot odds of 0.085 were better and we smile and calls his bet knowing that he made a big mistake making a so small bet.