There are two main ways to sum a column or row with SUM in Excel:

1. Using AutoSum:

This is the quickest and easiest method for simple sums.

* Click on the empty cell below the column or to the right of the row you want to sum.
* Navigate to the "Home" tab on the Excel ribbon.
* In the "Editing" group, locate the "AutoSum" button ( Σ ).
* Excel will automatically detect the range of numbers you want to sum and insert the formula `=SUM(A1:A10)` (assuming your data is in column A from rows 1 to 10). You can adjust the range if necessary.
* Press Enter to confirm, and the sum will appear in the selected cell.

2. Using the SUM function manually:

This method offers more flexibility for specific ranges or calculations.

* Click on the empty cell where you want the sum to be displayed.
* Type the formula `=SUM(`, followed by the cell range you want to sum.
* Separate cell references with commas if it's a discontinuous range (e.g., `=SUM(A1:A10, B5)`)
* Alternatively, you can click and drag your mouse to select the range you want to sum directly in the formula.
* Close the parenthesis `)` and press Enter.
* The sum of the selected range will be displayed in the cell.

Tips:

* You can use SUM with other cell references or formulas within the parentheses for more complex calculations.
* SUM works with numbers, text that can be converted to numbers, and logical values (TRUE or FALSE converted to 1 or 0).
* If your data contains text that cannot be converted to numbers, SUM will ignore those cells.
* Consider using error handling functions like SUMIF or SUMIFS for specific criteria-based summations.