Multi-Step form posting w/ $PHP_SELF

I’m creating a mult-step PHP quote form that is going to be posting to itself, but I’ve never tried it this way, but needs to be done this way. I’m fundamentally sound with PHP, but have some questions regarding this method. The steps are as follows:

  1. Personal Information
  2. Delivery Information
  3. Product Information
  4. Confirmation > Submission

I’m comfortable enough with being able to do this in one step, but not more than one. My primary question is, how do I get the form to go to the next step, and so on, after the user has filled out the first step? Would I implement hidden input types? If so, how and where? Any help would be appreciated.