Why are there so many stars in the sky?

The gas and dust get hot when they fall into the middle and stars are made. The reason there are so many stars is that the universe is very big and contains lots and lots of gas and dust, so there are lots and lots of stars. All the matter in the universe (gas, dust, planets and stars) is called mass. read more

As for why there are so many stars in the galaxy - well that's the definition of a galaxy (just like you could say that the reason there are so many trees is that you are in a forest). Stars form out of giant clouds of dust and gas in galaxies. read more