I'm not in the camp of the people who think you need an actual job first. I think you can learn it all online. It's a different path, but you're a different generation, and right now, I frankly think the economy's so bad that the "experience" jobs of yore just aren't there for many people. Not that you shouldn't get a conventional job if you want to or need to, but I don't think it's necessary in order to learn.
What do you need to learn to earn by AdSense...?
1) How to produce good content. That means how to create content that people find valuable via video, text, photography, graphic arts, or whatever. You don't have to always produce it for your website indefinitely, but doing it yourself is the cheapest route when you're still learning and can teach you what to look for if and when you hire others.
2) The rules. Laws you have to follow. FTC guidelines about testimonials if you're in the U.S. All the terms of service and program policies of the AdSense programs and related programs. So many folks don't know the rules - which are not always intuitive - make mistakes, and then lose access to some of these programs for life.
3) How to market. Who your target audience is. Old marketing principles and new marketing principles. And learn long tail theory - read Chris Anderson's The Long Tail. It's not exactly the online marketing bible, but it does present a starting point for looking at the Internet as an entirely different economic playground.
4) This one's kind of fuzzy and tree-hugging, but what the heck: About people from all over the world. If you're from the U.S., you may have a U.S.-centric outlook (see? I'm displaying mine by assuming you're an American). But of course the Internet is the playground of the planet, and there are different attitudes about things, and eventually we'll be talking to people without a language barrier, and even when the same language is spoken differences can be huge, and it's a good idea to get a jump on understanding it all so that you can conduct business worldwide.