Well, first of all, open up Computer>Local Disk C:>FeralHeart.
You should see a Screenshots folder. This is where all of the screenshots you take will go when you press prnt scrn on your computer. If you don't have a Screenshots folder inside the main FH folder, try making one and name it "Screenshots".
Then go in-game and press the prnt scrn button on anything random. It should take a screenshot and save it to that folder. If not, try reinstalling because the original Screenshots folder may have been deleted somehow. Reinstalling will replace it.
Hope this helped.