Just as a tip, remember that if you enter in an empty cell "=XXX(" (unquoted) and press the "fx" button at the left of the edition bar text box, you'll be prompted with the function wizard which shows every argument, gives a brief description of the function and by the bottom left link lets you access the built-in or online help. It works for any function.
SUMPRODUCT is basically the sum of ranges multiplication, element by element, where you can select elements by condition for each range independently. And use many aggregate functions as well, but start with the main idea.