I'm a relative novice in using Excel so pardon me for the layman lingo used here.
Consider this scenario:

A B C
1 10 12
2 12 14
3 14 16
4 16 18
5 18 20
6 20 22
7 22 24
8 . .
. . .
. . .
. . .
. . .
. . .


I want to compute the average of the values in the A and B columns. So in cell C1, I type the formula =AVERAGE(A1:B1) to obtain the average. But now I have thousands of cells to compute, so how do I go about doing so without having to manually type the formula in the respective C cells?