If you are new to writing online you may find yourself navigating the various sites and wondering which one is the best to write for. That, of course, depends on you and your interests.
I often hear new writers ask which one makes the most money. Again that depends on you. But, we can address that later. Right now, the important thing for you to do is gain an understanding of your options for making money as an online writer.
Basically your options are: being paid for page impressions, which mean the site your write for pays you according to how many readers visit your work, by revenue from ads clicks, or outright payment. You may see terms like "unique visitors"--a fancy way to say that you won't be paid for every time aunt Betty visits if she chooses to read your article a 100 times a day, or Google Adsense and Google advertising programs--those little ads that show up beside your article.
My article The Top Five Ways Writers Make Money Online explains it all in more detail, so I won't repeat myself here. If you are serious about being a successful online writer and making money from your writing, this a good place to start.