How would I randomly generate a 3d world in Godot?

I am trying to create a grid-based randomly generated world. The way it will work is by randomly choosing from an array of possible world chunks, and then spawning 9 of them in a 3x3 grid. However, to do this, I need to know how to add nodes to an array, as well as move around a child node, either before or after adding it to the scene tree. I know the theory behind all of this, I just need the commands used by Godot to achieve this. Thanks! Also, If you need any additional information to answer, please tell me.