There are tons of opportunities on the web to start new businesses. An online business is not so different from a "brick and mortar" business model. For your start-up venture; the same principles apply.
If its a product you want to sell, Ebay is a great starting point.
Set aside several hours to browse around the site. Click on all the different buttons to access and learn about eBay's various features. Read the news announcements, check out the help pages, surf the discussion boards, take the online guided tours, and study the listings. A great place to begin is with the eBay Learning Center, which offers free audio tours and online courses.
Learn all about eBay University They have sessions that are held across the country 30 weekends a year. One of those sessions of eBay University is likely to come to an area near you. eBay is a huge site, but it's well-organized and easy to navigate. Take the time to get familiar with it before you get started, when you're not under any pressure to buy or sell.
There are many Seller Forums on Ebay that you can participate in. Once you're familiar with ebay, you can start planning your business on eBay. Decide if your goal is a full-time operation or something you can do part time. Start with partime and don't be discouraged if you do not sell your product at first. There are many veterans of Ebay, so if you are just starting out then you have a lot to learn.