Do you have to pay federal and state tax on stocks you sell?

First, it depends on whether you have a gain or loss on the stock. If you sold it at a gain, then you have to see if it can be offset by losses on other sales. Assuming not, then yes - the gain would be included in your taxable income. As for how much federal tax you would owe - that depends on how much other income you have and whether the gain is considered long-term (asset was held for more than one year) or short-term (held for one year or less).

On the state side - that depends on your state. Some states charge no income tax, some states use a reduced rate for long-term (but not short-term) gains, and some tax all gains the same as other income.

The short-answer to your question, however, is - generally yes, you do pay tax in that situation.