Calculate your outs, win probability, and pot odds in Texas Hold'em.
An "out" is any unseen card that would improve your hand to a likely winner. To calculate your win probability, you need to know how many outs you have and how many cards remain to be dealt. On the flop with 47 unseen cards and 2 cards to come, your probability is approximately outs x 4. On the turn with 46 unseen cards and 1 card to come, it is approximately outs x 2.
Flush draw (4 to a suit): 9 outs. Open-ended straight draw: 8 outs. Gutshot straight draw: 4 outs. Two overcards: 6 outs. Flush draw + open-ended straight: 15 outs. Set to full house or quads: 7 outs. One pair to two pair or trips: 5 outs.
Pot odds compare the size of the bet you need to call against the total pot. If the pot is $100 and you need to call $25, your pot odds are 25/(100+25) = 20%. If your win probability exceeds your pot odds, calling is profitable in the long run. If your win probability is lower, you should fold (unless implied odds change the calculation).
Implied odds account for money you expect to win on future streets if you hit your hand. If you are drawing to a nut flush, your opponent will likely pay off a large bet when the flush completes. This means your effective pot odds are better than the immediate math suggests. Implied odds are harder to calculate precisely because they depend on reading your opponent.