You can limit how many users can sign up for a time slot by clicking the Limit each time slot checkbox and typing the number of time slots in the limit field [1]. If you selected the option to have students sign up in groups, this field reads as Limit each time slot for x groups.
To make the appointment slots public to students in the course, click the Allow students to see who has signed up for time slots that are still available checkbox [2]. Selecting this option also allows students to see comments other students add to their appointments.
If you want to limit the number of appointments available, click the Limit participants to attend [number] appointment(s) checkbox [3].
Note: When using the group signup option, only one group member needs to sign up for a time slot on behalf of their group. Each member in the group will see the appointment on their own group calendar.