A star is mostly made of helium and hydrogen atoms that are attracted to each other. In the middle fo this ball, gravity creates strong pressure which causes the atoms to move closer and closer together. These movements gradually result in the formation of a ball shape. Essentially, stars ar giant, glowing balls of gas.
We name 3 different types of stars:
1. Standard stars
Those are stars that are not part of a constellation, like the Big Dipper. They're located between those constellations.
2. Constellation stars
You'd be able to name one of the main stars of a constellation of your choice. You'll find further information about constellations here.
3. Binary stars
A binary star system consists of two stars surrounding. Further information can be found here.