Voluntary.
That's what the United States is... voluntary. Just look at the income tax. It's voluntary. Just because you don't know how to volunteer out.
"Volunteer out" is basically an oxymoron. You don't need to "volunteer out" of a voluntary system, you simply do nothing.
Using a legal system to achieve certain ends only proves that you submit to the authority of that legal system.
While in simple terms this is true, odds are that you ave volunteered in. Volunteering out has to do with showing the IRS that you are not volunteering. Generally they won't bother with you if you have never signed any of their forms.
If you ever signed a personal tax return, a W-4 form, a W-8 form, or almost any other IRS form, the IRS understands that you have volunteered in, even if you don't understand it this way. There are ways to sign the forms that show that you don't volunteer in. But if you don't sign that way, the IRS is accepting that you know what you are doing and have volunteered to become part of their tax paying system.
If they come at you through the courts, you need to know how to tell them you have volunteered out, or never volunteered in, in the first place. Since they want your money, they will not make it easy on you.
If you have never signed any of their forms, the best thing you can do is don't start signing now... unless you want to volunteer in, that is.
If you have signed a W-4 or W-8, and you want to start showing them that you are volunteering out, do a new one, signing your name, non-assumpsit, and n/a on any appropriate box, and "EXEMPT" on any exempt line. Non-assumpsit essentially means "no contract." Since the income tax is voluntary, show them that you are not making an agreement with them, even though you are signing their paperwork.
Why might you sign their paperwork at all? Your employer might require, say, a W-4 so that you can get a job. Even though the paperwork is between you and the IRS, your employer has made himself into an IRS agent to an extent, and he has to collect paperwork for them. When you sign "no contract," you are showing both the IRS and the employer that you have volunteered out. Your employer is not supposed to withhold if you file EXEMPT on the no-contract form.