Basically, with an online subscription-based business, you'll be asking people to come to your site and pay you an ongoing fee to regularly access your content. The recurring fee could be monthly, yearly—however you want to set it up. It's not that much different from the way a newspaper or magazine might sell subscriptions of their publications to their readers. Technically, then, the online subscription model is a subset of e-commerce: You have to have a site, and you have to have the ability to accept payments, with the main difference being that you don't have to maintain an inventory of products and you don't have to worry about shipping.
What you do need to do, however, is make sure that whatever you're asking people to subscribe to (access to your site, an online newsletter, etc.) is updated regularly, provides value, and gives access to content your audience can't find anywhere else. That's what makes the online subscription model so difficult: With so much content on the Web—literally hundreds of millions of sites, blogs, and networks—most people are used to getting their information for free. Convincing them to pay for content on your site takes a very special kind of sales pitch.
You'll have to provide something unique. It could be your writing style or particular viewpoint, insight into topics that can't be found anywhere else, access to your site design, or unique online tools that can make a user's life easier. Whatever it is, there needs to be a value that people can't find anywhere else to build a profitable subscriber base.
While building a subscription-based business might not be the easiest way to make money online, it also might not take too many subscribers to turn a profit. For example, 1,000 subscribers who sign up at $10 per month will bring you a gross income of $10,000 per month, or $120,000 per year. Increase the amount you charge and the total number of subscribers, and you're bottom line increases as well.