Once you have all of your wooden pieces cut it is time to assemble.
For my project I needed to piece together the back panel. I'll walk you through the way to glue finger joints together as it will be the same process throughout the construction of the box.
Place a dab of wood glue in each valley point of the finger joint on each panel.
Place the panels together adding the sides of the boxes (without glue!) to make sure there the back isn't glued together so tightly that the sides won't fit in on final construction.
Clamp the pieces together to encourage a good glue connection.
At this point you will want to finish the back panel with a technique of your choosing.
I decided to cover the back with the same fabric that I used to re-line the suitcase. I added a bit of glue around each of the finger joint points for shelves and placed the set the fabric in place. Once the glue was dry I went through and cut the fabric away from the holes so I can place my shelves using a straight edge blade and scissors with a sharp point. I also trimmed away the fabric from the finger joints around the edges that will join with the side. After doing a couple test fits and adding the sides in for proper spacing it became clear that I needed to glue the fabric along the edges as well or they would be pushed into weird positions during final construction.