Let's look at an example on how to determine Pot Odds for Texas Hold 'em. The same logic applies to Omaha and Omaha High Low. Pot Odds are based on the number of "outs" you have. Let's say you get AcKc in your hand. If you assume a pair of Aces or Kings will win the hand then the aces and kings left in the deck are outs. You have to decide if the top pair is strong enough by reading your table, and seeing what has flopped before you can mark them as outs. Lets assume you think one of those pairs will win it, you now have 6 outs, the other three A's and the other three K's. When wouldn't they be outs? Let's say four hearts came on the board and you are facing the river, it is likely that your pair won't be good enough as it takes only 1 heart to beat you, now you have no outs.
Let's go back a step and say the flop had 2 clubs. There are 13 of each suit in the deck. With the 2 clubs showing and the 2 clubs in your hand, that leaves you with 9 outs. If you still think High Pair will win it, you add the 6 from pairing those up and you have 15 outs. Let's take it a step further, if in that flop where was a J & Q, the 10 has also become an out which would give you the straight. No 10s are showing so there are four of those bringing your out total number of outs to 19. To help assist you in calculating pot odds based on outs; you may want to get a poker odds calculator.
Now let be clear about when to use outs. You do not need to calculate outs for texas hold 'em when you think you already have the best hand, then you just raise (or slow-play if you feel the need). You can use outs to determine if you should raise (when checked to), the more outs you have the more willing you should be to throw in a nice bluff(especially if you are last to bet) that has a good shot at paying off through hitting the card; or everyone folding. Outs are most powerful when you are being raised. It is here you can use your outs to determine if you have pot odds, and should call or get out.
Turning outs into pot odds is the next step when determining if you should call a bet. Lets say you have 9 outs. That gives you a 20% chance of hitting the desired card and taking the hand. You are raised $100 after the turn. You are going to get your card needed 20% of the time, that is 1 in 5. So your pot odds number is 5. You only call the bet if you are going to win 5 times the bet if you hit your card. If the pot is only $300, get out. You only chase where the money will make up for the number of times you fail to get your card. So pot odds tells you if you come out ahead long term, no need to wonder if you should chase anymore, use math guarantee long-term results. Mastering pot odds is important, but it won't help you if you are not playing the best starting hands.