There's loads of advice and insight on this board, but I wouldn't call any of it legal advice. For that, you need an attorney. But a little knowledge can get you a long way, so here's a start....
Alot of PTOs incorporate in their state. This is a formal status that must be applied for (usually a small fee) and renewed annually. Incorporation typically provides some level of personal liability protection. In addition to incorporating, many PTO's apply for federal recognition as a non-profit charity, 501c3.
Most PTO's do work that the IRS considers qualified for 501c3 status. There is lots to know about why and how to get 501c3 status, but the basic rule of thumb is:
Is your annual gross (not net) income normally greater than $5,000. If no, then you can do your work without filing for 501c3.
If yes, then the IRS expects you to formalize your group as a 501c3. The application is called form 1023. The one-time fee is either $150 or $500, depending on the finaancial size of your group.
Lots of PTOs operate without incorporating or filing for 501c3, whether or not they "should". As your group gets more informed about this issue, you'll be better equipped to decide what course of action is right for your group. YOu're started the educational journey. Good luck. It's a little daunting, but many many regulary ol' PTO volunteers have learned enough to educate their memebers and get 501c3 status.
One really good source of info is the PTO Today Getting Started Guide. It has a whole lot of advice on setting up and formalizing a PTO. The link to the guide is
forms.ptotoday.com/store/store.html