@HannahGR
You will file and pay income tax only in California.
You may have to pay sales tax in any state that you deliver products to, depending on either the number of sales or the dollar amount of sales in the state. Each state has different requirements, and different sales tax rates. In many states there are also local sales taxes, so the sales tax might depend on the specific location that the product was delivered to. The multiplicity of rules and rates is why you need software or a service to handle the sales tax for you.
You will definitely have to pay sales tax on any sales delivered to California, because your business is located there. And California is one of the states that has lots of local sales taxes, so the sales tax rate depends on the specific delivery location for each sale. The sales tax rate can even be different in different parts of the same town, because there are special taxing districts for specific purposes.
