Hey,
I happened to stumble upon this post, and my recommendation would be just to start by selling things around your home. I started out by doing this, then I moved onto selling ebooks. After you establish a decent ebay seller account, you can start moving into physical stock. Once you get proficient at selling on ebay, you should be able to choose a niche and see if you can profit on it!
Feel free to PM me if you have any questions, and I hope this helped you. Good luck on eBay!