magnetism is the force and pull of the north and south pole.If two of the same side of pole are facing the same way the will not connect.Why because the both are facing the same pole the both are connected to the pole say north they will not connect two different poles will connect since ones facing one way and the other is facing the other.
density is the mass.To simplify comparisons of density across different systems of units,it is some times replaced.
heat is something that can be used for energy and is warm
A insulator is a thing that its electric energy does not flow freely.Also a perfect insulator dose not exist.But you can make insulator with glass paper etc.
A conductor is a object or type of material which permits the flow of electricity.It Also produces energy.