Here's how to add all numbers in a column or row in Excel, including blank cells:

Using the SUM Function:

1. Select the cell where you want the sum to be displayed. This cell will typically be below the column or to the right of the row you want to sum.
2. Type the formula: In the formula bar, enter `=SUM(`.
3. Select the range: Click and drag to select the entire column or row you want to add. Alternatively, you can type the cell range directly (e.g., A1:A10 for cells A1 to A10).
4. Close the parenthesis: Type a closing parenthesis `)` after the cell range.
5. Press Enter: Hit Enter on your keyboard to execute the formula.

Explanation:

The `SUM` function in Excel adds all the values within the specified range. By including blank cells in the range, they are treated as zero and contribute nothing to the final sum.

Example:

If you have a column A with numbers in cells A1, A3, and A5, and blank cells in A2 and A4, the formula `=SUM(A1:A5)` will add the values in A1, A3, and A5 (assuming they contain numbers) and return the total, even though A2 and A4 are blank.

Alternative (Using AutoSum):

1. Select the cell where you want the sum displayed.
2. Click the AutoSum button: On the "Home" tab, locate the "Editing" group and click the "AutoSum" button (Σ symbol).
3. Choose "Sum" (Optional): By default, AutoSum selects the range directly above or to the left of the selected cell. If necessary, you can click the down arrow next to the suggested formula and choose "Sum" from the list.
4. Press Enter: Hit Enter to accept the AutoSum formula and calculate the sum.

AutoSum is a convenient option that simplifies the process by automatically selecting the appropriate range for addition.