I always first gather all my items before I start soldering. Instead of the PCB you could use a breadboard.

I would recommend doing them in this order.

1. Relays
2. Resistors
3. Uno Stackable Headers
4. Screw Terminals

In my assembly video that I made I did the Stackable headers first and it worked, but I think this order is better.

Given that the project at the moment does not have good connectors and just screw terminals I just cut some extension cords up so that I could plug the lights that I bought into them.

I am planning to disassemble some things that do plug into the wall (phone chargers, power towers, etc.) to see how there assembled so that I can do this step better.

The code that I used can be found in my GitHub for the project and in particular at this link: https://github.com/PhysicsUofRAUI/decoration_control/tree/main/examples/five_relay_5s_blink/five_relay_5s_blink.

If you have never uploaded code to an Arduino Uno I recommend reading this article first: https://learn.adafruit.com/ladyadas-learn-arduino-lesson-number-1/upload-your-first-sketch

This step will look differently for each person and which decorations they want to control. For my demo it meant stringing a bunch of lights up and connecting them to the board. For others they might have 5 pumpkins with an electric lamp inside to turn on and off. Still others may have lights and pumpkins.

I am really not sure what all this could be used for which makes it fun for me.