Step 2 - Soft black "skid pins" go into middle square holes on red connectors NOT round hole. Launcher mount fits into the yellow connector exactly the same way a rod would fit in the same connector - lay the Launcher mount on top of the opening next the opening in the yellow connector and press it into place.
Steps 1-3 - If the TNT blocks are shifting while you are building (Steps 1 - 3), you can remove the green tile pieces and 1 x 2 green bricks and place the TNT blocks directly on the base. Assemble the structures that snap together separately and then, while holding the base firmly in place attach them to the base. Examples - Steps 4 and 5; the 2 parts of Step 6; and Steps 7 through 12.
Step 4 - Use 1x2 gray bricks with holes in this step - red arrows hide holes. Take moveable pieces off to assemble structure.
Step 12 - Orange Adapter Rods connect into 2nd holes on gray bricks