Once you have downloaded the RAR file(s) from the host site, you'll need to de-compress (extract) the file(s). You can use any ZIP software for this, I recommend 7-Zip because its completely free unlike Win-zip which only offers a free trial. Once you have extracted the files, they will most likely be .BMP .GIF .JPG .PNG .TGA or .TIF files.
Once you have these files, upload them via the menu on the left in the Torishop. With my account, I have to click 'Textures' and upload them via that, but my brother has to click 'Activated' then upload via that, so try both.
Hope I helped :3