If you are planning to setup one online store and sell something online, you need the below:
1) Domain name – As usual, any online business you need a domain to represent you or your store. If you want to register a domain name, I would recommended you www.namecheap.com.
2) Hosting – This is something that is common too where you need a server to store your files, many places are offering hoting now and www.sitehost4u.com will be the one that I am currently using.
3) Online Catalog – Definitely you need to have a catalog for your visitor to browse through your products before they decided to buy or not. One of the free services that I like to use will be Google Checkout, a free services that Google is offering. Every successful transaction, Google will charge 2% to 3% which I think is reasonable. As long as you have a gmail account with then, then you can setup your Google Checkout account.
4) Payment Gateway – If you are using Google Checkout, then its included payment gateway. If you are using some other catalog that didn’t comes with payment gateway, then you have to host one payment gateway. Usually I am using paypal.com or 2checkout.com.
One you have the above mentioned 4 items, then then next is hire someone to desing a website for you before you can open your store for public. If you can design web pages, you can do this your own too.