Any folder called what you like.

Inside that, a folder called 'runtime'

Install any files you like into that. In fact, I have a 'test runtime' that is empty. Any of the old Bitrock installers I just point at that and let them do their thing (although doesn't work for base DAZ characters like Victoria 4... they need the Poser.exe present to install files). Basic structure inside a runtime folder is: Geometries, Libraries, Templates, Textures.

Inside Libraries are the folders that show up in the Poser library (surprise!). These are: Camera, Character, Face, Hair, Hand, Light, Materials, Pose, Props, Scene.

You don't need all of them, but you'll probably end up with them at some point.

Mostly let things go where they want, but some things I'd suggest:

don't move or rename geometry. Poser will still work, it's just slower because it searches. Same for Textures.

You can move materials/pose(mat) files into the corresponding character file to have all in the same place. Locations that have a character and a stack of props can be moved to a single place, as can the mat files for clothing items. Same for hair (textures matched to the hair/character).

A bit basic, but should get you started, and was quicker than looking up the tutorial for you...