This has been a question also made by some people here on BHW. It takes time for you to start earning from a blog. It's not an overnight process.
For now, if you haven't started yet. Plan on what will be the name of your blog, the niche you want to go into, SEO strategy (you can read a lot of free online references), posting frequency, etc..
Once your blog was launched, as much as possible, focus on writing or creating great articles. Articles that will be useful to all the people who visit your website. Fast forward.... Once you establish a decent amount of traffic and build a group of followers. Apply for an Adsense account, monetize your blog and start earning from it.