If you can write you can earn money on the internet. Now that is an extremely substantial statement. I suggest that you read it again.
Blogs are personal journals that are frequently updated. Basically, you would choose a niche market and then setup your blog around that and update it frequently.
There are two popular platforms that you can choose. If you are a newbie then the Blogger platform that is owned by Google is more suitable. Alternately if you have a bit more technical experience then the WordPress one is a better option. It comes with a MYSQL database and also has a lot of very advanced features that are very useful. If you are serious about building a blogging business then I recommend this option. However, you may need to hire a technical expert to set it up as it can be very involved.
I suggest that you register your own domain name and get your own web hosting. The main reason for this is that if your site is hosted on Blogger or WordPress and you violate one of their terms of service you may get your site suspended. Also later on you will lose your search engine rankings if you migrate and all your incoming links still point to your hosted blog.
The trick to succeeding with this method online is that you need to deliver quality content. Content is king and this is what will set you apart from the many other sites online.
Finally, you can monetize your site by using Google AdSense or doing reviews of affiliate products related to your niche market.