Here is a step-by-step guide on how to fix a cell in Excel:

1. Open the Excel file that contains the cell you want to fix.
2. Click on the cell you want to fix.
3. In the formula bar, add a dollar sign ($) before the column letter and row number of the cell you want to fix. For example, if you want to fix cell A1, you would add $A$1 to the formula bar.
4. Press Enter.

That's it! The dollar sign will keep the cell reference constant even if you copy the formula to other cells.