Actually Rob, knowing when to fold is the easiest decision to make: just fold every hand. In a cash game you will only lose your blinds if you fold every blind. You won't win any money, but you'll just lose your blinds. I actually know some players who go to a certain casino that serves free food to its players and they will sit at the table, lose their blinds, just to order their food. Then they will "sit out" and eat and then leave. They literally can have a $25 or $35 steak and lobster dinner for the price of $5 which is the $3 and $2 blinds.
But a more practical answer about folding: In Texas Hold'em you are dealt two cards. Let's say your cards are the 7 of diamonds and the 2 of spades. And you have several players ahead of you at the table who bet first. And they are betting big. You would fold if all that big betting went on pre flop because you know 7-2 offsuit are very weak cards.
Another example: You have pocket kings (king of clubs and king of spades) and the pre-flop betting is made and the dealer flops the first three community cards on the table and they are Ace of hearts, Queen of hearts and Queen of diamonds. And before it's your turn to bet two other players are betting big. This is when you have to think that they might have an ace (two aces beats two kings) or they might have a queen (three queens beats two kings) or perhaps the players have two hearts and they are on a flush draw. With two more cards to come (the turn and the river) you might want to fold those kings if the other players are betting big. But if they are not betting big and you wouldn't be losing too much you might want to stay in the hand to see if perhaps another king hits on the turn or the river, or if no more hearts are showing on the table.
In poker you have to do a lot of thinking. It's not just the cards you have -- it's what the other players have.
In video poker a 7-high flush is a winner, but in live poker your 7-high flush would lose to an 8-high flush.