To use the SUM function in Google Sheets to add up numbers, follow these steps:
Open your Google Sheets document.
Select the cell where you want the sum to appear (e.g., Cell A1).
Type the equal sign (=) to start the formula.
Type SUM( in the cell or the formula bar.
Select the range of cells that you want to add up. You can select a contiguous range (e.g., A2:A10) or separate cells using commas (e.g., A1, C3, F5).
Close the parentheses by typing ). Your formula should now look like "=SUM(A2:A10)" if you selected a contiguous range.
Press Enter on your keyboard.
The sum of the selected numbers will now appear in the cell where you entered the formula.