To import appointments from other calendars, such as Google Calendar, iCal, Outlook, etc., to your Bookitit Booking Calendar, you must first open the calendar external to Bookitit, export the appointments in .ics format and attach it to the calendar you want.
To do the latter, access from the Control Panel to My Schedules and click on the sixth action (ICS import).
From here, click on Browse and select the file you just exported in .ics format.
Now, all appointments you have already created in other calendars will appear in your Bookitit calendar.
It is important to remember that this is an import and not a synchronization. In other words, only appointments already made will be imported, but appointments made after this import will not be updated. If after the import, new appointments are created from your personal calendar in iCal, Google Calendar, Outlook, etc., they will not appear in the Bookitit calendar.