Markings should go in the C/FeralHeart/Media/Textures folder.
Items should go in the C/FeralHeart/Media/Items folder.
And be sure to do the coding on those. I believe users put the coding in files that come with the download. You'd just copy-paste those into the right file (For markings it's the markings.cfg file, and for items it's the items.cfg file, both found directly in the main FeralHeart folder).
Hope this helps