The columns (K21/Puchacz/Perkoz) show the aircraft type. If you're booking for the first time, this doesn't matter, and you can pick any aircraft. The rows show the time of day (AM / PM) and the instructors name. If you are new, its it's important you do not book the instructors prefixed with 'XC', as these offer a different type of training. Note that there is a link at the top of the page to view dates further ahead than the default view.