If you've heard stories about how you can start a blog and make a living from it in a few months or less then don't believe them.
It takes a while to get search traffic to your blog and takes time to build up quality content. You should have the patience to wait at least 5 years before seeing any significant money from your blogging efforts.
You'll work long hours in the beginning without any pay. But if you stick with your blog and continue promoting it and writing lots of great content the payoff can be big in the years too come.