Those 'items' are called meshes. You can install them into your game by opening up that file (it's usually a .zip or a .rar) with either WinRAR or 7zip (I use WinRAR so I'll explain the steps using that program.)
When you open the file you should see the .mesh and texture/material files in it. Drag those into your FeralHeart > media > objects > my_objects folder. If you see a .object file in the .zip or .rar, put that in FeralHeart > media > objects.
I simplified the steps to shorten everything up, but if you're confused I can go into detail with it.