Event Booking

When Booking a event on the calender does it automatically be on that event when you log into Zwift?

Yes. Zwift knows that you have booked that event. If you start a ride you will get a reminder with around 15 minutes to go asking you to join the event. This means that you can warm up before entering the event start pen.
I think meet-up reminders are around 5 minutes before the start time.