It is vital that you know you are getting good value for your bets, so you must understand Pot Odds
You are dealt Ace, seven of hearts and a club.
Flop comes two hearts and a spade.
Pot is $120 and it will cost you $20 to bet. Do you bet or fold?
Of the 52 cards, you know 5 of them, (two in your hand and three in the flop),
leaving 47 unknown. Of these 9 will help and 38 will not.
the success odds are 38/9, nearly 4/1.
The Pot Odds
are 120/20, 6/1.
Whenever the Pot Odds are greater than the success odds - you bet.
You're sitting with an open ended strait, The pot is $200 and it will cost you $25 to compete in the pot. What do you do?
You can see 5 of the 52 cards in the deck, leaving 47 unknown.
Among these unknown cards there are 8 cards which will fill your strait and 39 which will not.
Your success odds are therefor 39/8 or nearly 5/1.
Looking at the Pot , the odds there are 200/25 or 4/1.
You are getting 4/1 from the pot, but only 5/1 to win - a sucker bet.
A gut-shot strait - forget it, unless the win odds are better than 11/1, very unlikely.