The Events feature has a calendar that shows all upcoming events and lists past events.
Volunteers can see shift availability from the overall Events Sign-ups calendar page or when you click on the actual event page itself.
If the shift has unlimited slots then the event will also be available. There is a color coded legend at the top right of the events calendar that says if an event is available, full, or if you as the volunteer have signed up for that particular event.
To sign up you click on your desired event and click on the shift's sign up button on the right. You will then be prompted to fill out who you are by either registering as a new user or signing in as an existing volunteer. The setting can be configured so that the person signing up does not need to be a member of Track it Forward and does not need to register, but does need to provide some basic information like phone number or email.