You just signed on today. Did you sign up for managed payments? You can't sell until you complete that requirement.
https://www.ebay.com/help/selling/getting-paid/start-getting-paid-ebay?
After you complete your registration, you may want to try this to help you be a better seller:
https://sellerschool.ebay.com/
It can help you with all your questions concerning being a seller on ebay. Good luck.