You need to rephrase your question mate. First of all, there are tons of businesses and i dont know which one are you talking about. do CPA, affiliate marketing, email marketing <--- now i still dont know what you are looking for. if you clarify it maybe i will put in some thoughts
affiliate marketing could be a great start, you can easly sell some copys and the joy the first sale brings you ...
Cheap & easy: bung up a wordpress blog about something you are interested in (the hard bit is the on page seo and choosing your niche keywords but loads of help on here for doing that) and sell either your own e-book or go to clickbank and find one you like thats relevant. Then sprinkle a few PPC ads and ,bingo, you have a potential income stream. Should take about 3 or 4 hours to get it up and running to begin with. Then work hard optimising, promoting and marketing it. But if you find some ad-free free hosting it won't have cost you a dime.
Make up a site and put some ads and also get products sale from clickbank and place them too in your site and keep on updating it.. then only you would be getting repeated users and increase in your page view, get google adsense too.. now you can do up your business
Free online business? Set up a free blog and put up adsense on it, and optimize it - lots of hard work! This is a real business, not get-rich-quick, just so you understand. Paul
Try internet marketing and also try blogging. Then, join forums related to your online bussiness to seek advise.