Taxable income = Total income - Standard deduction
Look up tax due in a table.
Subtract taxes already witheld, pay (or refund) the difference.
In most states you also have to file, but this is normally just transcribing a few totals from your federal filing and then computing the state tax due, normally just a simple percentage multiple.
But also, taxes can get complicated, I'm just suggesting that for many people, with typical incomes and employment, they are not.
When I was in middle school (1970s) we learned how to file a tax return. For some reason this is no longer taught today.
We have the same problem in Norway; youngsters aren't taught proper private economy at school, just the "normal maths." Which leads to people getting into financial trouble because of stupid stuff. :/
Thanks for updating me on the US tax system! Hope all is well over there! :)