To make money with Adsense you need to first have an Adsense account. You can apply for one here: http://www.google.com/adsense
Once applied for you need to wait for adsense account approval, that usually takes about 48 hours. Then when you have your account up and running the next thing is to begin making money.
To make money online with your Adsense account you'll need:
To have a website, blog, or a YouTube account. The way you make money online with a website or a blog is by monetizing you website content in other words you display Adsense ads on your website or blog and every time someone clicks that ads unit you earn money! The another way you can make money is on YouTube by monetizing you videos, it works similar to monetizing your website content.
So this is pretty much how to get started making money with Adsense.