Some US states require that online marketplaces (for example, Etsy) collect and remit sales taxes on behalf of their third-party seller transactions. This means that any sales you make through these marketplaces will be taxed for you automatically. Unless you have nexus in these states, you will not be required to do any additional remitting.
If you do have nexus in these states, please see further information here.
Please note that you must acquire a sales tax permit (seller permit) in order to collect sales tax in your store.