Where the majority of 'beginners' go wrong in poker is that they simply call too much in general. When we are 'out of position' and are willing to call a bet from our opponent, we should be looking at betting our hand rather than check-calling! So why is this? Winning money in poker is the main reason everybody plays, but how do we win money/chips in a hand? Well, there are 2 possible ways:
1) Holding the best hand at showdown.
2) Making our opponent fold his/her hand. The likehood of our opponent folding his/her hand is what poker players call "Fold Equity"!
let's see an example: We are holding AJ and our opponent is holding 22. The flop is dealt and runs-out as shown below:
This flop isn't great for our hand (as we have not flopped a pair), but given the weakness of our opponent's hand, if we bet, our opponent will likely fold his/her hand and we will win the pot. Fold equity increases the deeper our stacks are in relation to the pot size. This is simply because the greater the amount of money our opponent needs to put in the pot, the fewer the number of possible hands our opponent is likely to continue with (range - gets narrower). Conversley the less our opponent needs to put in the pot, his/her range will become wider and there will be less fold equity.
Let's go with another example: You are holding AQ with a stack of $100, and our opponent is holding 99 with $100 stack, the pot in the flop is $500, the flop comes down as follows:
Even though our opponent's hand is weak in this board, he may not fold given the stack sizes to the pot. Now let's think the same situation but with a pot of $100 and stacks of $500. Now it is more likely our opponent will fold given that the money he has to commit to the pot is multiple times greater than the current pot size.
Another good use of Fold Equity is when holding a draw, because by betting with a draw we can either make a bigger pot for when we hit it or make our opponent fold a better hand than our high card. An example would be: You are holding J10 and our opponent holds 88 and the flop comes:
Even though we only hold a straight draw we can take the pot away from our opponent, using fold equity, by betting and make him fold his hand weak hand.