The Appointments report counts the diary itself. Find it under Reports in the sidebar (owners only).
Pick a date range and you'll see how many appointments were booked for it, how many completed, how many were cancelled or missed, and the share booked online - customers booking themselves on your page or website rather than the desk keying them in. Each figure is compared against the period of the same length before it, a chart shows the diary day by day, and a busiest-times grid shows which weekdays and hours your appointments actually start - darker means busier, and it's the picture to roster from.
The online share is worth watching: every percentage point that moves from the desk to your booking page is time back at the counter.
Export CSV downloads the day-by-day table for the range on screen. For what missed visits cost you, see the No-shows & protection report.