Somehow I wanted to write something from universe… not really I am still sitting in my hometown so here it is:
Well, stars (as our Sun) DO have beginning and end as you probably heard already. It can have different length.
First of all there have to be material. I mean lot of material because as you know our sun is huge. (Sun is bigger that 90% of stars)
This material comes from other stars that are dead now and theirs material probably came up from Big bang.
There are extremely large clouds that are called Molecular clouds. In them is lot of stuff and mostly H2.
If there is enough stuff at one place (it is really dense) it can make up planet which is either stony or made from gas.
If there is enough stuff it will make even larger gas planet than Jupiter or Saturn.
At that point all of this H2 will be pulled toward the center with magnificent force. That will create heat because atoms will be brushing against each other. If there is enough heat termonuclear reaction will occur which will normalize that pull of gravity and whooo! we have new born star!
Termonuclear reaction will change Hydrogen to Helium. Helium is heavier so it will go toward center and just a little bit of Hydrogen will be left on the edges. If the star is enough heavy it will start to change Helium to Carbon or Oxygen (I think). It will continue with couple of rounds until there in the middle is Lead (Pb). Than it will never be able to go forward and the life cycle will kind of end. Few more termonuclear reactions will occur (That is called red giant because it will greatly gain volume and the it will lose it) but then gravitation will win and if that star was small (even like our Sun) White Dwarf will be the END.
White dwarf is only really dense and hot piece of stuff.
If it was heavier.
Neutron star (made of only neutrons) will be the next stage. It extremely dense thing with tremendous gravitational field.
The last thing which can happen is Black hole, you can read about them in one of my first posts, they are absolutely awesome!
PS: if white dwarf gains again enough mass because of some stuff from space it can heavily explode into Supernova