How do plants turn into coal and create iron bridges from thereon?

I need a step by step process, please.

Plants grow and then die. The dead plants lie in the ground and start to rot. The decaying matter has layer upon layer of soil and dust laid on it over millions of years the pressure and heat builds up turning decaying plant matter into coal. People dig out the coal. The coal is used to fuel furnaces which smelt iron from iron ore. Iron is used to construct bridges.