Cron tabs give you the ability to run a set program or script at a certain time.

To set one up, go into your cPanel account and press Cron Jobs.

Select Advanced.

You will be presented with 5 columns for the time/date etc, and then one for the command.
Entering a * (star) in one of the time fields means every day/minute etc.

For example:

10 0 * * * would mean every day, at 10 minutes past midnight.

You can also write */10 to mean EVERY 10 minutes/days etc.

Or, you could write 10,20,30,45 to mean at those times/days etc.

In the command field, enter the command you wish to be run. For example, to run a php script at a certain time, enter php /home/username/public_html/script.php