What version of SSDT/BIDS are you using (2008, 2010+)?

The grouping pane typically is at the bottom of the report design screen. It isn't a popup. See the attached image. To add the total right-click on one of your data cells and select Add Total which will add a total row below but within gthe group., repeat with other cells that you want totaled.

The image Finished Report Design shows what the designed looks like with the totals added. At least my interpretation of what it should look like.

Grouping and totaling is one area where I don't think they made the product better with the 2008R2 release. It isn't as intuitive or simple as it used to be.