How to setup Google Calendar


I have been trying to setup Google Calendar in Appointments+ but the instructions in the settings are rather limited. I have found a WPMU video but that shows a screen that I do not have, probably an older version:

I've searched for a post on the support forum but there are 50 pages found no matter what search query I use. Can you please help me set it up? A link to up to date instructions, including what to do on the Google side of things would be great too!

The idea is to setup the calendar so that Appointments+ does not allow clients to book on dates and times that are "busy" in Google calendar.