Google Adsense is not a get rich quick scheme. If you're coming from the 'make money online' mindset and believe you'll make a lot of money by building a bunch of worthless sites and plastering them with Adsense, I'll be straight with you, you won't learn a whole lot from this tutorial.
It works because that's the core fundamental of business. A business offers something of value and earns money by bringing that value to others.
Value can mean different things; a site that serves as a resource, writing that's entertaining to read, tools that people actually use, or a site that's just plain useful. The point is, your site's got to have a purpose to it other than just to make you money.
What Is Google Adsense?
Google Adsense is a legitimate shortcut for many online publishers because it allows them access to hundreds of thousands of online advertisers. If you're an Adsense publisher, advertisers run their ad on your site and when a visitor clicks on it, you earn money.