If you are wanting to start using databases to drive aspects of your websites, I thoroughly recommend two tutorials.

The first - PHP/MySQL Tutorial - Part 1 assumes absolutely no knowledge and walks you through setting up the database, inserting information, displaying data, selecting specific records, error trapping, updating and deleting records. It's very straightforward and surprisingly simple.

The second is at MySQL Tutorial - Introduction and again assumes no knowledge but covers everything in more detail and continues to a more advanced level. I probably refer to this more often than the first tutorial now.

Tizag also has a great PHP tutorial if you need a starting point there.

And of course, you could always refer to the PHP and MySQL manuals.

Anyone else got any favourites?