I hear people talking about it all the time in class. But I don't know what it really is. It bothers me so please answer me.
Fusion occurs deep within a star and results in tremendous amounts of radiation.
The rest of the star is kept from collapsing by the resulting radiation pressure. The fusion stops when all the fusible elements have been used up, then the star collapses in on itself due to its own gravity. It all also depends on the original mass of the star. Some supernovas leave behind a neutron star, pulsar, or maybe a black hole. Although I think that John's note may have gotten to the heart of the matter, you may not have understood all the words.