For those that want to manually add challenges you can easily do this by clicking the "Add New Challenge" link from under a ladder.

Next you will setup your challenge using the drop-downs.

NOTE: If a challenge isn't valid based on your rules, you must check the "OVERRIDE RULE?" to force the system to accept the challenge.  Once this challenge is entered, it will be entered into the system as an "ACCEPTED" challenge and both players/teams will be informed.