Step 10: Wiring up the transformer and dimmer switch
This photo is your wiring diagram. The black two conductor wire on the left goes to the wall plug, and the brown one on the right goes to the hot wire.
This photo is just to show what connects where. You should of course use the wire nuts that came with the dimmer switch (esp on the 120V connections) and/or tape to ensure that no bare wires touch each other, or you, or your pet. Be careful not to electrocute yourself or start a fire.