Go to Object Manager > Type > Groups > Press green + to create new group. Add a Name and then in the "Involved" add the People, Objects or other that you want to add.
Note: The Objects can't be multi-selected, you've to add them 1-by-1.
You can load the group into the Hourline, Object Tree or Personnel Tree.
From here you can then easily select a time range and e.g. run a Financial Report on the group members.
The Financial Report Designer window will then show the selected Objects from the Tree and the previous selected Financial Lines in Range.
You can also show the Group Members in the Toolbox > Objects > select the Group > right mouse click > Show Group Members.