The man who sold the world (Help)

New to guitar, I've been trying to learn The man who sold the world but I cannot for the life of me figure out how to strum the rhythm of the song.

The verse begins with an F chord but whenever I play it, it sounds completely different to how it's supposed to. Also, my strumming is utter dogshit and I have no idea why nor how to improve it.

The strings sound blunt and muted even though I'm only muting the correct strings