First point, it’s Studio 4, or DS4, not DAZ 4. Studio is one of several programs that DAZ produce, so best to be precise.
You can call your Studio content folder(s) whatever you want. You don’t actually need to know what folders go into a Studio folder, as with Poser the installers will create the folders for you when you point them at the content folder. The two folders you should be aware of are data, which is vital to the functioning of Studio and holds all the hidden detail on content, and Runtime, which is a Poser runtime used to install Poser configured files into. Data needs to stay where it is, but you can happily move Runtime into your main poser runtime if you so desire, just so long as Studio knows about wherever you put it. Other folders you are likely to see are people, cameras, lights, environment, location, hair, but none of these names are actually essential. The one essential point in this is that you have to tell Studio where your content and runtime folders are, see: edit/preferences/content library/content directory manager.
You will find a lot of Studio content tends to be installed into a folder called People - characters, clothes and textures for both can end up in there, but they don’t have to be in there, you can quite happily move and rename them, just so long as the data folder remains in place. However if you are using Smart Content you will need to update that with any folders you move around, so it’s probably best not to do it until you are happy that you understand things.
The one issue there tends to be with content installers is that some seem to be set up to install at the parent folder to the content folder, and some at the content folder level (this is true of both Poser and Studio installers, particularly freebies). What this can lead to is nested content folders, or folders that should be in the content folder being the next level up. The solution is the same in both cases - drag and drop them to where they should be. If you run an install, and suddenly find data and other new folders in the parent folder of your content library that’s a sure sign that this has happened, just drag and drop them into the content folder. Similar sort of issues for runtime - one thing to watch for is a nested runtime within the Studio content folder’s own runtime,that needs to be dragged up to content folder level so it merges properly with the existing runtime.
If you’re just getting started then most of this detail isn’t actually necessary, just start by adding an extra content folder, telling Studio about it, and installing something into it. When you start up Studio again you should see the new folder appear in the Content Library tab, and the new content should be accessible via both Content Library and Smart Content.