the poser 9 folder is one "runtime folder", the "downloads" is another that you can add stuff you have downloaded to. Some people install stuff just into the main poser runtime, although this makes it harder to find things as the amount content you download increases.

The folder icon with the man running on it is for adding additional runtimes that you have created to the library eg Poser 9, Downloads, Renderosity Content, Daz Content, whatever you like.

Daz Studio 4.8 and 4.9beta, Blender 2.78, Sketchup, Poser Pro 2014 Game Dev SR5 on Windows 8 Pro x64. Poser Display Units are inches