In order to find your equity, or the chance that you will win the hand as a percentage, you must be familiar with the concept of how many outs you have to win. If aren't familiar with these topics, do not worry as they are easy to learn.
For example: If you have 4 cards to the flush on the flop, you have 9 outs (cards that turn your hand into a flush).
As a quick calculation to find an estimate of your equity, you would do
9 outs x 4 = 36% (turn)
9 outs x 2 = 18% (river)
Basically, you work out the number of outs you have and multiply them by 4 if the turn and river are still to come.
And with only the river to come you multiply the number of outs by 2.