QuickSel Loops

can someone explain me a bit better than the manual what the QuickSel Loops are in the LENGHT MENU? (upper/ lower row), and also in the loop setting on that page 1-256 is only for the loop start, is there a way to set the loop end? 

thanks

They define the track length.

The track length is also the loop end

Best Regards, Thorsten.