How do I create form groups, roll groups, and how do I activate students to be enroled
Form Groups (UK English) and Roll Groups (US English) are the same thing. You can add them under Admin > School Admin > Manage Form Groups. Form groups are specific to a school year, so you need to re-add them each year. Once they are added, you can go to Admin > User Admin > Student Enrolment to add students to a form group.