Lorna Mitchell has a new post today spotlighting a handy feature of the phpMyAdmin tool - the visual designer view. It allows you to build (and see) the relationships between your MySQL-based application's elements.
I'm happier at the command line, but needed some graphical representation of information and easy ways to export example queries for the book I'm working on. I noticed that phpMyAdmin now has a Designer tab, which shows relationships between tables and allows you to define them.
She includes two screenshots of the process of setting up a foreign key on two tables. You can find lots more articles related to the designer view here.