Bookings can be found on the event's booking tab or the bookings tab on a person's profile. You can search for them by booking number or the name of the person who made the booking. The booking page shows when the booking was made, the payment type and the tickets booked. The number next to the booking name (in this case the number 2 next to John Smith) is the booking number that was provided to the person when they made the booking, you can use it to quickly look up their booking.
Editing the booking will let you add a note and change the ticket type of each ticket.
The side panel is displayed on the right hand side of the page, if you are viewing on device with a small screen such as a tablet or phone you can access it by tapping
Check in can be used to manually check someone in to an event with scanning their tickets. If you need to view a person's tickets (maybe to print them) then tap "Download tickets".
"New email message" will let you send a message to the person who made the booking, and if they didn't receive their booking confirmation email along with invoice and tickets then tap "Resend confirmation email".
If you are an admin you will also so Latest activity, tapping this will show the people that have viewed this booking and all the changes that have been made.
If the booking payment was made by credit card and a payment service other than PayPal then you can also issue a credit card refund. You can find this option in the side panel.