what licenses are need to open an online store?

No "licenses" are required under federal law. Depending on the nature of the business to be conducted and whether you will have a retail presence in your home state, you may be required to comply with local business licensing requirements (you do not specify where your principal office will be). Regardless of where you operate, you will need to set up your systems so that you can collect and remit sales taxes when you make sales to residents of your home state. Your accountant can assist you in doing so.