If you create a new “Self-Book” template, you will will have the option of changing the "Self-Book” form to keep bookings to your Calendar from being automatically accepted. Using “Booking Processing” will hold any pending booking made to your Calendar from posting until you approve it.

If you have "Hold for approval" turned on you'll need to go to the "Review Bookings" panel in order to approve or reject "pending" bookings. We can send you an email notification when visitors have submitted a booking to your calendar, but you can also see what bookings are "Pending" by looking at your calendar. 

For "Suggest an Event" and "Make a Reservation" template you can see the number of pending bookings show up next to the Self-Book button above your calendar. For "Book an Appointment" and "Group Sign-Up" events you'll see a red "Pending" link next to the booked event. See the image below: