RSR files are no longer used in Poser so there is really no need to create or use them.  You have legacy models in Poser that you can use and modify through morphs to create your own characters.  But if you are interested in creating your own from scratch, then you need other applications like Blender (Freeware) for such endeavors.  You will need to be very specific about your intentions because Poser is not really a model-creation program.