I'll tell you a little secret about online marketing. There really is no "secret". The 90% of profits that you see being made are with simple, boring, low-hype strategies that anyone can figure out. These "secrets" that most people are seeking really only matter once you're already making money, which oftentimes are unique ways to maximize conversions, etc. But in the beginning you need to just master the basics.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.