This book is intended for anyone starting out with PHP programming. If you've previously worked in another programming language such as Java, C#, or Perl, you'll probably pick up the concepts in the earlier chapters quickly; however, the book assumes no prior experience of programming or of building Web applications.
That said, because PHP is primarily a Web technology, it will help if you have at least some knowledge of other Web technologies, particularly HTML and CSS.
Many Web applications make use of a database to store data, and this book contains three chapters on working with MySQL databases. Once again, if you're already familiar with databases in general and MySQL in particular you'll be able to fly through these chapters. However, even if you've never touched a database before in your life, you should still be able to pick up a working knowledge by reading through these chapters.