On reports: when you create and filter a report it "automatically" creates a User Group.
After creating a report that you need, where you have filtered all of the students with "MATH"(Subject Areas), selected only the "Freshman"(Student Demographic) who have visited the center for "Tutoring"(Service Type) more than 3 times on a Visitor History report you decide you want to save that group and call them "Freshman needing Math Help."
You can do this after you run that report by visiting the User Accounts > Groups section on the left-side navigation panel. Once there simply click on the Report Generated Groups tab, then click on the report you just ran, and click edit. At this point you can name the group and hit save changes and the group will now be available for you to use as a group filter in future reports.