A complimentary how-to start a small business online is Start Up Nation
view linkAlso here is MicroSoft's webstite to help small businesses start up online
view linkSo there's lots of resources out there. Just do your homework and compare services vs costs.
But first you have to pick your product(s) and make sure you can get your hands on enough inventory in a timely manner ... especially if it's creative stuff you make yourself. I still it'd be a good idea to start at flea markets, gift stores (always looking for unique inventory), craft fairs, etc. to see what actually sells, what the competition is and maybe even to get new ideas. Check out the "Farmers Market" thread here
view link for other ideas.
And someone here (thank you whoever you are) pointed out that you don't even have to open your own vendors booth, you can ask if the established vendors are willing to feature your handmade cards, jewelry or other crafts. If they like your stuff, that's a first great sign that you've got a sellable product!