HI! here we have a picture of the big band where everything started, today we are gonna talk about stars
stars are born in a nebula which is a BIG gathering of cloud and dust!
when gravity causes all that dust and gas to condense and spin it can heat things up to extreme temperatures!
when the temp. reaches 10000k it's called a protostar! HOWEVER if the mass of the star soon to be is not enough then it becomes a brown dwarf!
when temp. reaches 10 million K hydrogen begins nuclear fusion to form helium, this is when the star really starts to shine and appears on the H-R diagram as a main sequence star. our sun is one of these!
so your star is getting old and it's hydrostatic equilibrium isn't as effective as it used to be, well depending on your star's mass determines what it's doing, see normal sized stars' cores collapse and their atmosphere expands turning helium into carbon but bigger stars turn helium into iron!
as this goes on for some time suddenly BOOM PLANETARY NEBULA or in bigger stars' cases SUPERNOVAAAA, and for some EXTRA heavy stars they turn into black holes!
lastly your normal sized star has basically shed it outer shell and the only thing left of it is it's core, no more fusion, earth sized but still HOT and eventually it's light will die out and become a black dwarf. bigger massed stars turn into neutron stars! and that was basically all for the life cycle of stars!