What is the Box-O-Books program? I see that it has an annual fee of $8.00 How exactly does it work?

From the Help Center:

How Box-O-Books works: the Basics

• Once you enroll, your bookshelf becomes visible to other Boxers in the Box-O-Books area.
  • Your forum posts, your bookshelf and your PBS Profile will all have the icon on them.
• You get offers for swaps from other Boxers
  • Boxers who browse your bookshelf select books they want from you, then offer you a "Box swap"
  • When you get a Box offer, you can browse that Boxer's bookshelf and choose books for your Box from them
• You can also make Box offers to other Boxers
  • search all Boxers' books from the Box-O-Books area to find books you want, then choose a Boxer who has those books
  • or choose a specific Boxer's bookshelf to browse
  • create your box by "shopping" on that bookshelf and then make your offer
  • Box swaps are normally "even" (e.g., 4 books for 4 books), but they do not have to be. If you want to send out 6 books in exchange for 4, that is fine.  Each audiobook is generally swapped for two bound books, but this is not required
  • Requestor Conditions can be applied to Box-O-Books swaps
  • You can decline any Box offer at any point up until the time you have clicked to accept it
  • You are not obligated to accept a Box offer if you would prefer to get a credit for a particular book (or books) on your bookshelf.
• Boxers "negotiate" until they have reached a satisfactory swap; then they accept the swap and send the boxes to each other.
  • Your books remain visible on your regular PBS bookshelf until both Boxers have accepted a swap; then those books are removed from both bookshelves
  • If you get a "regular" for-credit request AND a Boxer request for the same book, you can choose how you want to swap the book: as part of a Box swap or as a regular swap for a credit
• Once a Box-O-Books swap has been accepted on both sides:
  • The package label is printed from the Box-O-Books transaction
  • PBS Delivery Confirmation can be applied to Box-O-Books swaps
  • Both Boxers mail the packages to one another.
  • When a Box is received it is marked received on the pending swap page;  there is a place to leave feedback on each swap.
• You can pause or suspend your Box-O-Books subscription at any time, for any length of time
  • Doing this does not affect ongoing (pending) Box transactions
  • Doing this also does not affect your regular PBS bookshelf