i think the way to do it would be to pick a cell under the numbers you want to avg. hit sum pick your range of cells you want to count then put / and the number of rows you have let me know if that works for you
For a quick sum of the values click on the column heading to select the entire column. Then at the bottom of your Excel screen right mouse click on the grey bar that tells you things like if num lock and caps lock is on. A list should appear that will let you select Average.