For a micro-business startup the internet can be one of the hardest places to do business - compare selling a handful of homemade jams on a stall at the weekend market to selling them online via a website or ebay. Payment and delivery raise can become a major task. Also, selling online you can have difficulty getting "seen" by potential customers - on the other hand, a weekend stall may supply a thousand potential customers, whereas the internet provides millions of potential customers.
One of the best features of doing business on the 'net is low start-up costs. Provided you spend the time, it quite possible to setup a complete micro-business (create your own website, register a domain, use a service such as KAGI or PayPal to process online payments and deliver virtual products online such as eBooks, software etc.) for less than the cost of renting a stall at a market for one weekend.
Once you get a bit bigger, it may be worthwhile to process payments using a online processor such as Advantage Processors. There are many different ways to process credit card payments.
It's probably best to start on a small scale to "test the waters" before spending too much money. If you're able, I'd suggest starting out with a virtual product (such as a small, useful software application or an eBook) that can sell for a few dollars and practice getting all the components of an on-line business put together for as little cash as possible:
1. Develop your product
2. Register an available domain name for $15 or so with Dotster.com or similar
3. Create a website with a free host such as 0catch.com - design the site with basic SEO techniques in mind
4. Create an account with KAGI and/or PayPal so you can process payments
5. Setup up ordering and delivery (eg. via email of a password to a secure download page)
6. Setup Sitemeter and Google publisher tools (Analytics and Sitemap) to track hits and performance of your site design
7. Throw in a little bit of affiliate marketing, AdSense, link exchange etc. to assist in promotion and revenue
This first attempt might be a flop - poor traffic and no sales, but it will be an invaluable learning experience for very little outlay of money (it will take a fair bit of your time however).
Once you've learned the basics you're ready to move up to a paid host, improved website design, and, if your sales start to take off, a more economical solution for processing credit card payments via Advantage Processors rather than KAGI or PayPal. Good luck!