How much income do you have to earn in order for the government to take tax from you?

I'm in the USA and here if anyone you work for, or any employer you work for who turns in the form to the USA to take out taxes then consider yourself as having paid some taxes. On your yearly IRS form in April that you fill out your income on there is a place that if you've overpaid your taxes then you get money back. You don't pay twice.