Create a formula
- Click the cell in which you want to add a formula.
- Type an equal sign (=).
- Type the formula.
- Press ENTER.
Tip To insert a sum for a range of cells automatically, select the first blank cell that follows the data you want to sum, either
below the column of data or to the right of the data in a row, click
AutoSum 
on the
spreadsheet toolbar, and then press ENTER.