Recreating Classic Electronics Kits
Add Spring Connectors
The first thing to go in will be the spring connectors. These can be kind of a pain, but one trick that I learned to make the whole thing easier is to use a pair of pliers to bend the end of the spring out. This gives you something to stick through the hole and gets the spring started. Once in, simply give it a few twists so that it screws its way into the cardboard. This is made less painful by grabbing the "wall" of the spring with a pair of needle nose pliers and twisting that way. Your hand is still gonna hurt after about 20 of them, though, so don't be afraid to take a break.
Once all of your springs are in place, you should have something that looks like the picture below!