Scroll down the page for a life of flashcards for you that cover sums of zero all the way through nineteen. Zero is the mathematical space holder. Like the guy in line that saves your spot. For instance the number 9302 means something entirely different than 932, doesn't it? In this case the zero says, "Hey, we have no tens place value guys!"
You will sometimes here 0 referred to as "nil", "Nought", or "O". In hockey we call it the "Goose Egg!"