Click Formula in the Data section of the Layout tab. First of all put your cursor in the cell where the value goes. For instance here we put it in.
Enter the numbers making sure that there is a number in each cell in the column.
Lets talk about the formula. Place the cursor at the blank cell of the first row then click layout Formula see screenshot. The first row is Row 1 the second row is Row 2 etc. When you first open the formula window Word defaults to the formula SUM ABOVE.