I have an Etsy store too and it's great. You do have to be 18 and the stuff you sell has to be your own. You can't use anyone else's patterns in your sewing. I think it's $.20 to list, not $.40 like Heather said but I could be wrong. It is a 3% charge on sold items and Etsy sort of does the advertising for you. I would encourage you to look at Etsy for a while before you jump in, the photographs need to be great because that's all a customer has to go on. You will get great ideas on how to display items on Etsy from other sellers. I found the hardest part was the banner for my store. I had someone help me with it but you can even buy one from other Etsy members for about $5. Payment is super easy, you need a paypal account and that's it.
You can check out my store too, convo me if you have any other questions. I would look around Etsy, the site is super user friendly and there is a great forum and blog on the site where there are answers to all your questions. The Etsy support staff is wonderful to, they respond within 24 hours and it's an actual person responding to your questions, not just some automated response. I love it and would highly recommend it.