What do I do with a booking when the guests arrive?

On Orders → Reservations & waitlist press Seat on their row and pick a table beside the button. Use No-show after a reasonable wait, and Cancel when they ring to cancel. Anything you get wrong has an Undo that puts the row back to booked. The three figures at the top count the day's bookings with covers, how many are booked ahead, and how many are waiting now.