Todd is giving a lot of great advice. I recommend reading thru it a few times.
Start out with a few products, listen to the feedback at craft fairs, and adjust what you make and the price point at which you can sell. Find something unique you can batch out easily with a decent profit margin.
My oldest son started making a few things last fall for our Church's craft fair ( 13 at the time ) , he ended up in two holiday craft stores selling about 10 different items. In one store he could only sell 3 items so he wouldn't compete with one of the paying crafters ( space was donated, so no complaints ). He ended up selling more $$ of his limited 3 items, none of which were over $20. He didn't have much inventory to start out with, so he struggled to keep up all season with demand. He has many more items now, and has dropped the items which didn't sell.
He is starting a pretty decent enterprise in his spare time outside of school, boy scouts, and basketball. He is still working on his web based store, but it is expected to be ready by the holiday season.
He has listened to the feedback from customers and others at craft fairs, and adjusted. Remember to be flexible and adapt.