Once you have added all the game details like course and game formats, move to the second page "Players and Groups". Once there select "Add players via Excel"-tab. Now download the template and fill it accordingly. Now you can upload your created import list, after this the players will appear in the "Player Pool", Player Pool can be found on bottom of the page.
Note: Save the Excel sheet in a "xls."-format (xlxs.-format is not supported).