At the top of the screen you can choose the date at which you want to play and you can set the number of golfers. The list will show you an overview of the available and non-available teetime slots. The times that show "9/18h" mean that you can choose between 9 or 18 holes for these times.
If you have set up a friendlist, the bookings of your friends will also be shown in the list. If the person has autorised you to add to his/her bookings, you can add yourself to the flight by clicking it.
Do not forget to take the time of sunset into account if you book 9 or 18 holes at the end of the day. The time of sunset is shown in the top right corner of the screen.