Several of the most common summary statistics can be found on the drop down menu under AutoSum. Any of these can be used by moving to the cell below the last data item in any column, selecting the drop down item and hitting enter. Sum will calculate the total value of all numeric entries; Average will calculate the mean value of those same entries; Count Numbers will calculate the number of numeric entries; Max will calculate the largest numeric entry; and Min will calculate the smallest numeric entry.
Tip The Sum button is also on the Formulas tab. You can work with formulas no matter what tab you work on. You might switch to the Formulas tab to work with more complex formulas.