Steps to sum the first 'n' values in a column or row, where 'n' is in a separate cell:

1. Select the cell where you want the sum to appear.
2. Type the following formula into the formula bar:
   Formula:

   =SUM(A1:INDEX(A1:A100, B1)) 

   - In this formula, A1 is the first cell in the range you want to sum.
   - A100 is the last cell in the range you want to sum.
   - B1 is the cell where you will enter the value of 'n'.
3. Press Enter to calculate the sum.

Here's how the formula works:

- The INDEX function returns a reference to a cell based on a specified row and column number. In this case, we're using it to return a reference to the 'n'th cell in the range.
- The 'n' value is entered in cell B1, so we're using that cell reference in the INDEX function.
- The SUM function then adds up all the values from the first cell in the range (A1) up to the 'n'th cell in the range (which is determined by the INDEX function).

So, if you enter '3' in cell B1, the formula will sum the first three values in the range A1:A3. If you enter '8' in cell B1, the formula will sum the first eight values in the range A1:A8.