Ok, I’m going to try and clarify a very confusing topic as it took me a long time to figure this out.
The folder structure is such that it supports two different formats, DAZ and Poser, and different generations of both. Having said that, it isn’t as bad as it could be under the circumstances, but it’s not the easiest to understand at first glance. So lets try to simplify it if we can.
First, in the DAZ program, the ‘Content Libary’ tab shows a semblance of the folder structure in your content ‘Library’ with two caveats. One, it breaks it up into two subgroups, DAZ Formats, and Poser Formats. Now these subgroups are obvious in the ‘Content Library’ tab of DAZ, but not so much at first glance in the folder structure. When you install DAZ, it creates the folder structure, then maps the ‘Content Library’ tab area to it in a pretty standard way. This can be later modified as long as one doesn’t move something DAZ expects to be a specific place, many items as long as they are in a general area, DAZ will find and display them, but others… if they are moved things break.
Most of this is pretty obvious to many of us so lets dive in.
The basic folder structure is as follows:
\Library (Main Folder)
\ {Invisible DAZ Stuff}
\ {Visible DAZ Stuff}
\ Runtime (Poser stuff and Textures for both)
\ {Invisible/Structural Poser Stuff}
\ Textures (Poser and DAZ textures go here)
\ libraries (note this is a second library folder… the Poser library.. and it’s spelled plural)
\ {Invisible Poser Stuff}
\ {Visible Poser Stuff}
The {Invisible DAZ/Poser Stuff} are support folders that get ignored by the DAZ Interface when populating the ‘Content Manager’ tab, thus invisible. They include \Readme, \Uninstallers, \Python, \Support, etc… For our purposes they can/should be ignored. If they are moved or modified by a user, things break.
The {Visible DAZ/Poser Stuff} are the folders that show up in the ‘Content Library’ tab and are what we can rearrange. In the case of DAZ, we can rearrange these any way we want and they will show up in the ‘DAZ Formats’ section of the ‘Content Library’ tab as we arrange them. In the case of Poser, there’s another caveat, the initial folders under \libraries are ignored except for specific named folders, such as \camera, \Character, \Hand, \Pose… etc… so if someone creates their own folder under \libraries such as \sites it will be ignored by the DAZ ‘Content Library’ tab. If we created that same folder under the \Library tab (note, Library is the main folder as seen above, not the \libraries folder which contains Poser specific items) it would show up under the ‘DAZ Formats’ section of the ‘Content Library’ tab. For it to show up in the ‘Poser Formats’ section, it would have to be made as a subfolder of one of the folders recognized for inclusion.. i.e. as a subfolder of \camera, \Character, \Hand, etc…
Now, another interesting point. DAZ doesn’t care what is put into which of the Poser recognized subfolders as long as the item is in a recognized subfolder or in a subfolder of a recognized subfolder. That means, one could put ‘characters (people, avatars…)’ in the \Hand or \Pose folder and they would show up and work just fine. A perfect example of this is the fact that Poser put shaders into the ‘Pose’ folder for reasons I won’t get into. People often move the shaders out of this folder and put them in a subfolder of the item they are shaders for, so if they are shaders for a character, they will move that shader folder out of the ‘Pose’ folder and into the folder of the character they are a shader for. When one goes to the ‘Content Library’ tab, these shaders would now show up under ‘Library\Poser Format\Figures\(character)\Shaders.’
Note also in the previous example that the ‘\Library\Runtime\libraries\Character’ folder maps to the ‘Library\Poser Formats\Figures’ area of the ‘Content Library’ tab. Yes, I didn’t mistype. The folder name (character) and the mapped content area (Figures) are not the same, and the folder ‘must’ be named ‘Character’ to be seen.
So, what does all this mean?
This might help:
\Library (Main Folder, don’t touch)
\data (invisible, structural, don’t touch)
\People (visible DAZ, not structural, rearrange, rename, move stuff and delete… whatever)
\Poses (visible DAZ, not structural, rearrange, rename, move stuff and delete… whatever)
\ReadMe’s (invisible, not structural, rearrange, rename, move stuff and delete… whatever)
\Uninstallers (invisible, structural, don’t touch if you want your uninstallers to work)
\{Anything Else} (visible DAZ, not structural, rearrange, rename, move stuff and delete… whatever)
\Runtime (Main Poser Folder, don’t touch)
\Geometries (invisible, structural, don’t touch)
\prefs (invisible, structural, don’t touch)
\Python (invisible, structural, don’t touch)
\Reflection Maps (invisible, structural, don’t touch)
\Support (invisible, nonstructural, don’t touch)
\textures (invisible, structural, don’t touch)
\libraries (Main Poser Folder, don’t touch)
\!DAZ (invisible, structural, don’t touch)
\camera (visible named folder, recognized… use however you want but don’t rename)
\Character (maps to Figures, visible named folder, recognized… use however you want but don’t rename)
\Face (maps to expressions, visible named folder, recognized… use however you want but don’t rename)
\Hair (visible named folder, recognized… use however you want but don’t rename)
\Hand (visible named folder, recognized… use however you want but don’t rename)
\Light (visible named folder, recognized… use however you want but don’t rename)
\Materials (visible named folder, recognized… use however you want but don’t rename)
\Pose (visible named folder, recognized… use however you want but don’t rename)
\Props (visible named folder, recognized… use however you want but don’t rename)
Since shaders are usually specific to an item I usually move them to a subfolder of that item. Cameras and Lights are usually specific to a site so I move them to a subfolder of that site, etc… Understand, everything coming in new will go in the place it was set up to go into, not your format so even if you delete unused folders, they will be recreated and repopulated when you get something new that the PA had stuffed stuff there. I didn’t bother explaining ‘Other Import Formats’, Products or Categories as they aren’t pertinent to this specific conversation. This is also a simplified version. That is, the areas marked ‘don’t touch’ can actually be touched ‘if you know a *lot* more about when it is/is not ok to touch them. Finally, this is all re: 4.0x.. not 4.5 and I can’t verify with certainty this all holds true in 4.5
* If anyone see’s anything the aren’t sure of, or are certain is wrong please feel free to ask/point out, goal is to elucidate 
