Slide the central channel over the channel of the side panel. Repeat for the opposite side.
At the tips of the panels slip the inner corner out over the outer corner. You will probably have a little stub left from the cutting to help here. This will tidy up the whole model, so do it for all four outer corners.
Slip the small bits into the opening on the front disk as shown to make some scary looking blasters.
Insert one Darth Vader and, like the Empire, you are all set to go out and fail to conquer the universe!
Next we make the shuttle...