Gather these parts
Glue the sides slotted into the back plate
Glue the previous assembly onto the base plate
Glue the stairs in as shown.
NOTE: the Top Stair is different from the others. The next to top stair may need to be trimmed on the back to fit. Dry fit and trim as needed with a hobby knife.
Prime with Rust-o-leum Profesional Enamel flat black and paint as normal with hobby paints.