It makes handling the rendering and display of forms, and more usefully, both client and server-side validation, quick and easy. This article will take you through the basics of that package. It assumes familiarity with HTML form elements, and reasonably basic PHP skills.
Thanks to the PEAR installer, setting the package up on your machine is a snap. They also point out that you'll need the HTML_Common package to get things working. They move on to creating a simple form - showing how to add the elements and what the output looks like. There's even information on adding input validation (you do validate your input, don't you?) and doing a bit of formatting for the layout of the elements.