A runtime folder contains one Libraries folder which, in turn, contains 9 other folders that appear in the Poser Library.  The folders are named in the following fashion:

Camera
Face
Hand
Materials
Props
character
Hair
Light
Pose

This hierarchy is a must, otherwise Poser will not recognize any installed content.  Some folders are obvious, Camera contains camera settings, Face contains facial expressions, Hand contains hand poses, Materials contains material files.  Anything that is rigged or conforming, like clothing or hair, generally inhabit the Character folder.  Props generally will contain non-rigged content.  This is also the place where dynamic clothing will reside.  Dynamic hair would go into the Hair folder, and the Pose folder will contain character poses or MAT Poses which TrekkieGrrrl briefly described. 

So far, are you with me?