08 dodge charger

Until you find the leak it cannot be fixed. Inspect the hoses, radiator, freeze plugs, heater hoses etc until you find the leak.

I see it coming from the thermostat housing but he took that off and said its a cylinder head or something. He said it was rust which means I need a whole metal cylinder. I have no clue what that is

You need to get a better answer than that. If the head gasket if leaking it will need to be repaired which is a fairly expensive job. Rust in the cooling system is another thing but it won't cause leaks.