You can have an automation add an event as its action. In the New Action dropdown choose Add Event:
When you add an event, you can set the Event Name, set it's Schedule, choose the Event Type and specify who are the Attendees:
You can set Event Types in Settings › Event Types if you need to add a new one first.
In the example above, I can create an automation that, upon booking a Wedding client, I create an unscheduled (to be determined) Engagement Session. The contacts that are marked as clients are attending and the name of the event is Engagement Session.
Other ideas:
Automatically add a sales meeting for 5 days after the primary session. Attendees include “Clients and Team Members” and call it “Ordering Session”.
Automatically add a call to the schedule one month before Wedding date and call it “Wedding Prep Call”