Use prompt to get input from the user. Remember that prompt returns string data so you will want to use parseFloat to turn it into a number before doing math.

var owed = parseFloat(prompt("How much owed?"));

var payed = parseFloat(prompt("How much payed?"));

var change = payed - owed;

alert("Result: " + change);

All i have so far are 3 variables.

var moneyOwed = x;

var moneyPayed = y;

var change = x-y;

I need to be able to input what they owe, what they are paying, and how much they get back as change.