just click on the field you want to sum
click on the sigma sign (blue E)
select the type as a sum
select the location as the group footer
it will create a summary that wikl appear on the group footer
This will only sum rows that fall into each group
the formula looks like this
SUM({table.value},{table.groupfield})
repeat the process for the grand total
it will palce the summary in the report footer
the formual look like
sum({table.value})