A cookie is a way you can store some information about a user visiting your site. The information is stored on the individuals computer, and thus you do not need any extra server space to customize a page for any amount of users you may have. To use Cookies there are two things you need to do, one is set the cookie, and the other is retrieve a cookie you have already set. Here's a brief tutorial on how to use cookies, and a couple of ideas which you can use cookies for.