What is the souurce of light produced by stars

To know this, first you need to clear your basic so I am providing you some information read it carefully and like my answer if you like it.
  What Is a Star?

A star is a fixed bright point in the night sky. That's what it looks like, but what actually is a star? Although stars might look tiny and insignificant, that's only because they are so far away. A star is actually a burning ball of hot gas and plasma like the sun. The sun is nothing more than one of trillions of stars spread across our universe. It only looks different because it's so much closer to us. 

Stars come in many shapes and sizes, from regular, ordinary main sequence stars like the sun to huge, red super-giant stars, or tiny, dim white dwarfs, or average size, but extremely bright blue-tinted stars. Part of the reason for this is that stars also go through lots of stages in their lives. The sun won't always look the way it does now. One day, billions of years from now, it will swell to form a red giant. And, eventually, once it burns itself out, all that will be left is a cool and dim white dwarf star. 

Why Do Stars Shine?

We already said that stars are burning balls of hot gas and plasma, and burning things do shine, just like how you can see around a campfire, but there's a bit more to it than that. Deep inside the sun (and every star), a special kind of reaction is happening. It's called a fusion reaction. At the very center, where it's millions of degrees hot, hydrogen atoms are being fused (or joined) together to form helium atoms. When this happens energy is released, and this amazing power source is what powers the sun for billions of years.