Excel function AVERAGE
The AVERAGE function returns the average of a series of numbers.
1st method
Select the AVERAGE function. Enter a data range in "Number1" and then click OK.

The average will be displayed.
2nd method
Select the AVERAGE function. Enter one cell in each box (up to 255 boxes will be added automatically) and then click OK.

The average will be displayed.

The 2nd method is generally used when the numbers to be averaged are dispersed on the sheet.