The back tray is assembled using two separate pieces. The top piece is usually black or white and there is a round outline with raised prongs in the center that hold the CD in place. There is a visible half-inch raised margin which is always on the left side of the top piece. The bottom piece is clear with one large hole on both the top and bottom left sides. Place the top piece over the clear piece.
Match the top and bottom edges and snap the two pieces into place. The CD tray will not snap into place securely if the edges are not matched up correctly. After you've snapped the center and bottom pieces together to form one connected piece, you can then snap the cover piece into place.
The cover is a clear piece that has two prongs that should both face to the left. Each of the top and bottom prongs on the cover piece has a round protruding groove. Match the top protruding groove with the largest hole on the top of the back CD tray and snap into place. In the same manner, match the bottom groove with the largest hold on the bottom of the back CD tray. Snap this groove into the bottom prong.
Most standard sized CD cases are universal in size. This means you can mix and match any of the three included pieces with another piece that didn't originally come with it. If the cover is cracked, remove a cover piece from another CD case. Snap into place matching the protruding grooves on the top and bottom prongs with the holes on the back tray. If the center tray piece is missing raised prongs, the CD will not be held in place properly. You can replace it with a center piece from a different CD case. Line up the center piece with the back tray, making sure the raised margin runs along the left edge. Finally, if the back tray is cracked, snap a back tray piece from another CD tray into place.