Start with the tenons, you don’t want to put glue into the mortise hole or it will push through onto the rounded tenon, then glue the middle shelf housing dado. You don’t need a lot of glue. Be sure to keep moving the joint to avoid glue freeze. Work on fitting the shelves and rails into one side before putting on the other side in place or else you won’t be able to assemble the project.
Tighten a clamp across the middle shelf to ensure the joints are fully seated, remove and do the same for top rail.
Zig zag the glue into the recess of your bottom piece, stand your frame upright and place into the bottom piece. Use the chisel hammer to fully seat the joints. Lay the shelf down on its face and tap the back of the bottom piece to make sure the joint is flush. Repeat this process for the top piece.
Before you clamp your project to dry, check that you are square by measuring corner to corner.
Make sure to line the clamps up parallel to the edge of your shelf to keep your project square. Leave overnight.
Remove the clamps and remove any dried glue marks with a sharp chisel. You can use a plane to take a shaving off the edges and also use sandpaper if you need to. Finish with 2 coats of shellac leaving an hour between each coat and your hanging wall shelf is finished.