Personal calendar functionality allows ANY agent to add a personal calendar so that tickets can be scheduled and synced with their own Google or Office365 calendar(s).
In order to allow agents to use this functionality, you will first need to switch it on under the "Settings" section like this...
Once it has been switched on, an agent will then have the option (on a ticket) of either creating an event on an existing global calendar or creating their own calendar to add it to like this:
They'll then see a popup screen where they can either create a calendar or connect up to their cloud calendar like this:
If they choose to sync up to an external calendar, the sync will work the same as for any global calendar as per this video and kb article.
By default, all personal calendars will be restricted so that only the agent who created it will be able to read or write to it. However, admins have full access to be able to change this in the calendar controls here: