As an example, if you go to this topic:
You should see a number of images. These images are the stencils. So what you'd want to do, is right click any of the images you want, and save them to a handy location.
ArtRage's stencil system can use these images, so then it's just a case of opening up the stencils panel in ArtRage, going to the category you wish to add them to ( or creating a new category via the menu ) then clicking "Add Stencil" and selecting the saved image.
If you're not seeing those images though, just let me know. Might be worthwhile making sure you're logged into the forums at the time but I doubt that's the problem. Hope that helps!