Set Kreg Jig to 1-1/2″ setting. Drill 1-1/2″ pocket holes on end of each 2×2, one per end. Attach to 2x2s with wood glue as shown above.
Cut 1×4 shelf boards with compound miter saw. Nail and glue to the inside of the project as shown above.
Cut 1×4 top boards with compound miter saw. Nail and glue to top with 1-1/4″ nails and wood glue.
If you wish to add a back, measure and cut from 1/4″ plywood and attach with 3/4″ brad nails.