You can select students and groups from the settings of the tool. Make sure you have selected at least 1 group to be able to choose students. After that, you can add up to 12 activities for the day. Decide how many students can participate in each activity. You can also choose the colors of the activities.
After you've set everything up, you can have students pick activities by dragging their names or you can do it for them. When you're ready to set up activities for the next day, click on the arrows to switch.