The very first step in becoming a federally-registered tax-exempt 501c3 is to determine that your group WANTS to be. Assuming that part is done (and that's not as silly a decision as it might sound at first), then on to the next step.
Your group needs its own federal tax identification number, also called the Employer Id number, EIN -- no you won't have employees, that's just what they call it. The information you need to get an EIN is on IRS Form SS-4 which you can access at
www.irs.gov. It's basically defining the name, contacts, and address for your group. The EIN is like your group's social security number --- just identification. Getting and EIN does NOT mean your group is tax exempt, non-profit, or incorporated. When you've filled out the info on SS-4, you can call the IRS as the phone # on the form, read them your data, and they'll give you an EIN over the phone. It's really that easy.
With the EIN, your PTO can open its own bank account, which is usually the next step.
In many states the next thing to do is to incorporate your PTO. The fee varies by state, but ours was only $25, renewable annually.
Now comes the harder part. Harder, not impossible. If your group wants to become a federally-recognized tax-exempt 501c3 charity, like many many many other parent groups, you need to file IRS Form 1023. The form is long, comprehensive and time-consuming, but not impossible. Some groups hire a professional to help them, but it's absolutely!!! something you can do yourself. Many groups do. There is a one-time filing fee of $150 or $500 payable to the IRS, depending on your group's size.
The PTO Today Start-Up Guide has step by step instructions and it's way cheaper than a tax attorney. It's available from this website.