Cron takes a Unix command and runs it at the set time. There are a variety of ways to trigger your scripts.
If you are using PHP, you can trigger a PHP script by setting the following as the command:
php -r path_to_your_script.php
Alternatively, if there is some function available over the Web, you could use curl:
curl "http://your.web.site.com/foo.php" >> /dev/null
If your script is a .sh, like idiot's, simply put the path to that script:
For a comprehensive tutorial on cron, see this article
You can also some kind of pseudo-cron script, like this one
(disclaimer: I haven't tested this - it could be a load of crap), which just uses visits to your site as a way for the cron to be triggered. If your server doesn't support cron, this is one way to do it.