Anyone making any money from blogging?

hi guys I have a small question about blogging I hope someone can help me here. I heard people talking about using blogs to promote their main sites. I would like to know more about that. I have a site where I write article on different topics, how can I use free blogs to promote that. I understood the part about linking the blogs back to my main site but what about the content on the blogs should I post the same article on the blog that I post on my main site? or how should I do it ? how many blogs should I create, I have articles on 10 different topics in my site.