Some of the more interesting customizations you can do with your Movable Type weblog require using PHP scripts, either on their own or in conjunction with the MySQL database. Some scripts are easy enough to install and require very little configuration. Others, however, require that you know something about how the script works, or how your MT database is set-up, or both.
Larry Ullman's PHP and MySQL for Dynamic Web Sites is a well organized, fairly comprehensive, easy-to-follow introduction to PHP and MySQL. Ullman expects you to know basic HTML and have had some exposure to programming. I took a basic Pascal programming class 25 years ago, but that's about it and I still managed to learn a lot from this book. The book is filled with examples and clearly laid out code. I had never heard of PHP or MySQL before using Movable Type, so the basic introductions to both were very helpful. I highly recommend this book if you are wanting to do more customizations with your MT blog that require knowing more about PHP or MySQL.