One of the handy features of Google Calendar within a Google Apps domain is appointment slots. In Google Calendar, Google Apps for Education users can create appointment slots. The appointment slots can be used to show people when you are available and allow them to sign-up to meet with you. The screenshots below provide directions for this process.
For Step 1 you need to be in either the Week View or the Day View
After the initial setup, all new appointment slots that you set up will be accessible through the same link.