Pascal's Wager is an argument for believing in God. He says that we should believe in God as a kind of insurance policy. The rough thought is that if God does exist, he would reward believers and punish atheists, and that gives us a pragmatic reason for believing in God, just in case. The calculator here just helps to calculate the expected risks and benefits of belief in God. It is a merely tool to aid thought on this topic.
You'll need to enter five numbers. The first number represents your best guess of the probability that God exists. You should enter a probability between 0 and 1, and the calculator will enter the probability that God doesn't exist for you.
Next, you'll need to enter the hypothetical payoff for believing in God if he does exist (heaven?), and the hypothetical payoff for believing in God if he doesn't exist (nothing? a nice community of fellow believers?).
Finally, you'll need to enter the hypothetical payoffs for not believing in God if he does exist (hell?) and the hypothetical payoff for not believing in God if he doesn't exist (more sleep on Sunday mornings?).
Those hypothetical payoffs can be any numbers you like, positive or negative. The important thing is just that they are proportionate to one another, not their absolute size (so entering 1, 1, 2, 2 is the same as entering 100, 100, 200, 200). I'm afraid the calculator can't handle "infinity" as a number, so if you want to approximate that you'll just have to enter something really big.