A star is mostly made of helium and hydrogen atoms that are attracted to each other. In the middle fo this ball, gravity creates a 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 aren't main stars 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: (Helpdesk "What's a constellation")
3. Binary stars
A binary star system consists of two stars surrounding. Further information can be found here: (Helpdesk "What's a binary star")