When I was a beginner, I heard all about how people put up websites full of Google "Adsense" ads and make alot of money from this. These ads are context-sensitive, meaning that they are related to the content of your web page. You let Google insert ads into your site's wep page and they pay you a few cents every time someone clicks on the ads.
I have a couple of Adsense ads on the top of my blog page. I make a few measly cents every day from these ads. Some people make alot more, depending on how much traffic they get at their site.
I just read a public domain report, that exposes the reason AdSense income sucks lately, even though many would be "gurus" on the net are pushing AdSense products like never before!
The report is called The Death of Adsense.
What's really cool is this guy (Scott Boulch, a "non guru") also explains how he went from a few hundred dollars in AdSense income to over $50,000 a month after he gave up AdSense!
He's closing the doors on the reports soon, so go grab The Death of Adsense while it's still a live link.