1. 1. You need to get a blog. You can get a free or self hosted blog. A self hosted blog is better because it give you more freedom to do what you want to do with your site.
2. 2. Put content on the site. You need content on the site for the adsense to work properly. The content can be of any niche, but adsense works better if you write about only one niche. For instance, if your site is about how to make money online, don't deviate and write about how to be a better student.
3. 3. Apply for an adsense account. Adsense now require you to have a website running before you get approved as an adsense publisher.