Explain what happens when a massive star ends its life as a supernova

The ultimate fate of a star depends on its mass.
A massive star ends with a violent explosion called a supernova.
The matter ejected in a supernova explosion becomes a glowing supernova remnant.

Toward the end of its life, a massive supergiant star has a central iron core, surrounded by a shell where silicon is being fused to iron, surrounded by a shell where oxygen is being fused, surrounded by a shell where carbon is being fused, surrounded by a shell where helium is being fused, surrounded by a shell where hydrogen is being fused.