Blogging can earn you a lot of money, or it can earn you nothing at all. It all depends on a huge number of factors.
Are you already a blogger? If so, in what niche? How long have you been at it? Do you write out of genuine passion and interest, or are you following trends? There’s nothing wrong with either of the two approaches, but the one you take will determine your overall money-making strategy.
If you’re only thinking of starting a blog, you should ask yourself, “What is my goal here?” Are you primarily stepping into this game to write about things you like (or dislike), or will earnings be your main motivator? Are you willing to spend hours researching successful bloggers before as much as writing your first word? Again, your answers will change your game.
Not to stretch this reply needlessly, the more time and effort you invest in your blog, the greater the chances that it will pay up in the long run. If you’re writing about something that you are genuinely passionate about, then all you should do is keep writing. You will want to grow a dedicated, almost fanatical audience that will stick with you and send positive word of mouth about your blog. If you simply want to make money from blogging, ape what the successful bloggers are doing, then use SEO and backlinks to push it as far up the rankings you can, and finally monetize the thing. Also, if you can afford it, consider outsourcing part (or all) of your writing.
So, yes, blogging can give you good earnings, but it will take a while. It can also give you zero earnings, while also taking a while.