When you printed the 3D parts, you have to place them on the base plate. On the base you can see four holes. These holes match with the holes of the two 3D printed rails. To connect it with the wood, you can use screws and some glue.
Make sure that the rails are open in the direction of the glass.
If you have done this you can place the glass fixer. Normally it passes good between the two rails.