The screen capture above shows a new variable (Totalcost) being created that will contain the sum of two database fields (PRO:QuantityInStock and PRO:Cost). The total is evaluated at the end of the report. This option is used primarily to obtain and print grand total(s) from information contained in the database.
The new variable was created by clicking the blue '+' button after highlighting Grand Totals.
If you need totals printed on each page the option 'Page Totals' will better suit your purpose, as it will gather the information when each page is generated and properly insert the value on the output.