In a happy home, I was a king I had a golden throne.
This is a hyperbole. The meaning of that is he could get whatever he wanted and he was happy with what he had.
Those days are gone, now they're memories on the wall.
This is a metaphor. The line compares to how memories are never forgotten and gone, like something stuck in a wall.
See heaven's got a plan for you.
This is a metaphor. The line compares to how everything seems as if it was laid out from the start and things are starting to get better too.
We ruled the world, I thought I would never lose her out of sight.
This is a hyperbole. The meaning of that is they felt like kings and queens of the world, they felt incredibly powerful, as if they could do anything they want.