In order to make an advising appointment, click on the calendar link for whichever professor you are interested in meeting with. A calendar will appear showing appointment slots.
To book an appointment, simply click one of the available appointment buttons and click Save. You can also edit other fields in the popup to make changes to the title, location, and event description.
You can cancel your appointment by deleting or declining the event on your own google calendar, which will appear as a decline on your calendar. The appointment then becomes bookable for future visitors to the appointment page.