Cronjob - Help a newbie!

[Nanook]

I have a website, which is running on a Linux server, with Direct Admin

I want to have a feature for users to create a page based on selections which will save to a directory, for example root/users/

I would like to create a cron job that will remove all files that haven't been accessed in 7 days to save disk space that will run once a week.

The trouble is I know nothing about Cron Jobs.

Is this possible?

If it is can you please take me through it step by step, this is my first attempt at a cron file and i have no idea where to start

Screenshot of my DirectAdmin Cron Job Control Panel:

Here (clicky) http://img340.echo.cx/img340/1049/cron3al.png (http://img340.echo.cx/img340/1049/cron3al.png)

Thanks for reading this.