1. Choose a formula or function that you want to use. For example, use the 'Sum' function to add columns or the 'Average' function to calculate the average of all the numbers.
2. Type the function into a blank cell. For example, type 'Sum(' without quotes to start the Sum function.
3. Type the column references, separated by a colon, then close the function with a closing parenthesis. For example, type 'a:b)' without quotes. Your function should look like '=Sum(a:b)'.
4. Press the 'Enter' key or click out of the cell.