That means you owe tax to your state which you must pay by April 15, 2021.
You must pay your state tax due using the state’s preferred method of receiving payment. For most states that will be by making a payment to the state’s own tax website, or by mailing a check or money order.
There are 37 states that have a state income tax. You are supposed to have state tax withheld from your paychecks if you live or work in one of those states. If you do not have enough tax withheld then you have to pay at tax time.