So the first step to creating an assembly is gathering all the parts. To begin, you have to create all the parts in NX, duh. Then, after they are all created, you open a new assembly and select all the parts needed.
Then, you can move them around to make each part easy to see. There’s really not much to it, but it’s the easiest step of making an assembly. Just gathering everything together. The hardest part is actually making some of the parts, but I’ve been assigned to do that so many times already that it’s become kind of natural.