If you're just making the move from procedural PHP development into the next level - object oriented programming - and are having a bit of trouble getting the hang of it, you might want to read this new tutorial from NETTUS.com introducing the topic.

For many PHP programmers, object-oriented programming is a frightening concept, full of complicated syntax and other roadblocks. As detailed in my book, Pro PHP and jQuery, you'll learn the concepts behind object-oriented programming (OOP), a style of coding in which related actions are grouped into classes to aid in creating more-compact, effective code.

He introduces the concepts behind objects and working with them in your code first then moves into how they relate to classes (with a housing metaphor). He talks about class structure, properties, methods (both magic and user-defined) as well as using __toString, visibility and using DocBlock comments in your code. They also have a comparison between procedural code and object-oriented code in the form of a few reasons to lean towards OOP.