I have no idea what I am doing wrong.When I press "fullscreen" or "F" on keyboard my whole screen goes black (only when i am in game)
I would really appreciate some kind of help

Well I solved the problem in case you're having some trouble with it aswell.It's actually pretty simple you just need to go to "properties" then u click "Compatibility"
after that u will see an option called "Compatibility mode" so just switch Windows version and one of them should work (in my case it was Windows 7)