Setting and playing around with cookies is a fun and useful way to save data on a user's hard drive, and can successfully store valuable information which may be helpful the next time they come to the site. Its fairly simple to set up, and even easier to read.

Learn how to build user-aware PHP scripts that can remember your user's personal settings on your website. Also a good introduction to cookies.

This tutorial will teach an alternative and effective solution to cookies in PHP which might actually be better for your website and security.

This is a basic sessions tutorial where the register globals are switched off.

Learn how to log users out of a system after x amount of minutes of inactivity. This is a great security add-on!