From the home screen, select Classes, and make sure you use the drop down to pick which class you're working in.
Select Assign Groups.
When you go to assign a group, you have the option to use existing groups that you or your district have created before or you can create a new group right on the spot.
If you want to create a new group…
Enter a Title for the group
Select a Color for the group
Now your new Group is created and you can use it at any point in the future.
To finish assigning the Group…
Select the desired Group (or Groups) from the list
Select the desired student(s)