To group students on your main roster. Go to manage students
To add one student at a time to a Group:
1) Select Settings (at the top of the page)
2) Click Manage in the Manage students box
3) Click Set groups at the bottom
4) This will take you to a page which lets you choose multiple students to put into a group
5) Click the triangle next to classes to see the students in them. Click the students you want to group.
6) Once happy with your selection, click Set groups at the bottom
7) If it's a new group, click Add to a new group, give your group a name and description if you wish. Click 'add group' at the bottom right corner. Alternatively, if it's a group that already exists, select your chosen group.