How did Zack Zuckerberg creat facebook and become a billioniar?

[Alex]

So i was just think how he created facebok and became a billioniar. why did he become a billioniar. how did he become rich. I am confused because i know that every one has a facebook account and stuff but its free to make a facebook account. so how do they earn money by giving out free accounts and stuff. and someone told me that they get money by advertising. but i dont think a lot of people would buy that many products or go on the ad or anything. so i am dtill confused. tell me everything to know about the guy and facebook and how they make money.