The AVERAGE function is extremely useful. As you might expect it takes two or more cells and averages them together to get a final result. One thing to keep in mind, a cell with the value or "0" will be computed as a zero, but a cell with NO value will be ignored in the average.
The AVERAGE function is used in many sheets:
=AVERAGE (A1, B12) averages cells A1 and B12 ONLY
=AVERAGE (A1:B12) averages every cell between A1 and B12 (or A1 THROUGH B12)