If you're in the process of prototyping a site or just need a lightweight storage tool for your application, you might look into SQLite. Fortunately, PHP has direct support for it and this great tutorial from ZetCode.com will introduce you to some of the basic concepts you'll need to get working (it's a bit older, but still very useful).

This is a PHP programming tutorial for the SQLite database. It covers the basics of SQLite programming with PHP language. There are two ways to code PHP scripts with SQLite library. We can use procedural functions or OOP objects and methods. In this tutorial, we use the classical procedural style. You might also want to check the PHP tutorial or SQLite tutorial on ZetCode.

They go through the basic installation (on a linux platform, but easily adapted to others) including changes to your php.ini and the creation and use of a first sample database. You'll find the interface very similar to some of its other RDBMS cousins with a few exceptions. They show you the CRUD basics - creating records, reading the contents of a table, updating data already there and deleting records. There's also a simple form tutorial that takes a name and gender and does the inserts.