There are over 5,000 stars that you can see in the night sky without a telescope. All of them are going through a cycle. A typical star starts out from another star that has ended its life and then when that star dies another star is born just like life on earth where animals are born, they grow old, then die. All different kinds of stars are very unique, very interesting to learn about and very important to the universe.
A star starts out as a cloud of dust particles and interstellar hydrogen gas. Next the star condenses under the gravitational attraction for each other. This happens until the temperature at the center of the cloud is hot enough to cause the hydrogen atoms to fuse and form helium. During the courses of stars lifetimes, they all change hydrogen to helium in thermonuclear fusion reactions in their centers.
All stars have different temperatures and are made up of different things. The temperature range from 3,000 to over 40,000 degrees centigrade. We live in the Milky Way Galaxy which has around 100 billion stars in it. It is 100,000 light-years wide and we are 28,000 light-years from the center.
The Big Bang Theory is a theory of how all universes started. It is very important because there where no stars before the big bang. The big bang is still expanding today.