First you need to create a Group and then add some Group members. Follow the steps described below to do this:
1. Tap on the "Settings" Icon in the lower right of the screen.
2. Tap on the yellow "+" button in the top right of the screen.
3. Give the Group a name e.g. "Math Class" then tap OK.
4. Tap on the Group you have just created and then the "+" button to add "Group Members".
5. Add names into the dialogue box, you can enter multiple names (up to 20 per Group) by seperating them with a "," (comma).
6. Tap the green "Play" button to randomly display the names in the Group.