Put your 2nd layer on. You will be soldering the positive (+) lead to the corresponding positive (+) lead on the next layer as shown. You may need to bend the wires so they meet.
Please note that the picture above is showing how to stack the layers. They have not been soldered together. If you connect one positive (+) to a negative (-) your LED will not light up in the end.
Do the same with the 3rd layer.
This is what you should have in the end. This is the one my mom did; a little crooked, but that’s OK. As long as all the soldering is good the LEDs will still shine. Set your LED “cube” off to the side. Let’s work on the PCB.