Suppose you are making yourself a sandwich. how many different sandwiches can you make if you have four choices in bread, two choices in meat, and five choices in cheese?

Yum, sandwiches. The answer is 40, but I'll explain why.
For the sake of this question, I'll assume we're only going to be using one of each item. It doesn't matter what order they're in, since a sandwich with wheat, bacon, and chedder tastes the same as one with wheat, cheese and bacon. That makes this a combination.
Now it would be extremely easy just to say "multiply the numbers, and that's your answer", but that would be the easy way out. So I'll explain why this equation works.
First, you can choose from 4 types of bread. That gives us four options. After that, we can chose from 2 meats. That's 8 different combinations, and we haven't even added the cheese. So now we get to choose from 5 of those. If we took those 8 different sandwiches and made one of each with each kind of cheese, that gives us 40 sandwiches.