First, go here, then log in to the Bell System, then click "Give Bells" on the side bar. Then it asks for the member's ID and the amount of Bells you want to give. By "Member's ID", I think it means the number that appears in their profile URL, not their actual username. So, for example, my profile URL is this: http://forums.the-bell-tree.com/profile/4012462/
So my member ID would be 4012462.