How to Make Money from Twitter? Is it possible to earn from twitter without any investment?

I heard that it is very difficult to earn money on twitter. How are many people making so much money on Twitter? I want to know how people are using Twitter to become rich. I am totally confused.

Are there any books or like which can teach how exactly to use twitter to earn much money? Please tell me what are the ways in detail, I am willing to pay if I find useful information on how to monetize on twitter.

Thanks.