Simply plug in your values to get your expected value!
When your expected value (EV) is positive, greater than zero, the mathematics of Texas Hold'em Poker say you should call because you will win the calculated amount over time, meaning it is profitable for you in the long run. Conversely, the opposite is true meaning that when your EV is negative, calling would be unprofitable for you.
Be sure to input your equity as a percentage. If you have a 42 percent chance to win, you would input 0.42 as your equity.

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.