Step 2: Wire up the relay board to arduino
Next choose which OUTPUT pins on the arduino you want to drive the relay switches, those get hooked up to the IN pins on the end of the relay board, and to the OUTPUT pins on your arduino.
At this point you should be able to turn pins on from the arduino and see the relays activate, they have a red status light so you know if they are "on"
The left-most 2 pins coming out of each relay are the 2 to use, those 2 will be 'closed' when the relay is 'on'
From the AC power, go in to the first pin on each of the first 3 relays you want to use.
On the second pin go out to the traffic light.
When the relay is on it should supply 120v across the relay to the christmas light bulbs in the traffic light.