"None" is a default field in the system and is there to make sure that you select an option of either Sender or Receiver. An option MUST be selected for each category item created.
Sender is the person who will be sending this payment on a recurring basis. Receiver is the person that should receive the payment for this item on a recurring basis. For example, if you are the person sending the Base Support payment you should select Sender as your role. If you are the person who should Receive the payment then you should choose Receiver as your role.