The Part "N" sides are glued onto the center "O" piece.
Look close and you can see how the glue was applied on the teeth, just on the sides that will make contact.
You can go light with the glue and add a fillet for strength after it dries.
Here's the "P" piece template to set the side angles.
While holding the template in place -
You can add more glue to the center joint on either side of the P piece. After it dries, remove the P piece and complete the fillets.
This assembly makes a parachute compartment. The chute is held in place during boost by the shorter, central fin.
Glue the two cardstock Q pieces on either side of the balsa R piece.
This makes a ejection bulkhead to go inside of the back end of the ST-19 tube.