hi. let me suggest a book that has helped me tremendously. its called PROFESSIONAL PHP PROGRAMMING published by Wrox (www.wrox.com). its a big red book with the pictures of the 5 writers on the front. retails for 49.99 usd. the ISBN number is:
1-861002-96-3
I find myself reading this book over and over and constantly referring to it as it is the best book I have ever seen for teaching PHP. (im even reading it again now :p)
As for functions, that's the focus of Chapter 7. it starts out with "what is a function" and by the end of the chapter has you writing (and understanding what you are writing) simple and more complex functions.
Chapter 9 is entitled "Object oriented programming" and is also complete enough to have you understanding what OOP is and implementing it effieciently into your code by the end of the chapter (and I had no clue what OOP was before I read the book)
all in all i highly recommend this book. not only does it cover what you wish to learn in understandable detail, it contains a weatlh of information and instruction that will be invaluable to you as a beginner on up to intermediate and advanced levels of php programming.
blue presley
blue928@carolina.rr.com