Unreal doesn't open .uasset files

Ok, so this just ■■■■■■ me off, im not going to lie. So when you export a project, it makes the assets .uasset files, which is files created by Unreal Engine 4. So when i for example download a grass asset from the internet, why cant i just drag that in Unreal and it works? It just says that it doesn’t regognize .uasset files and then it doesn’t work. Why haven’t you guys fixed this? I’ve seen other people complain and it can’t be extremely difficult to make Unreal recognize their own files?

I’m sorry for the rant or being mad, it just annoys me very much. And also when i drag the folder with .uasset files into “Content” where my project folder is, nothing shows up, so i have no solution to this. Also yet another problem, i moved my projects to another drive, and in the launcher i cannot just click “Browse” or something to tell the launcher that my project files are located there, very annoying aswell.

Any answer and help would be much appreciated.