To add, remove or change a cron job on your website, log into your Cloud Control Panel??(CCP), select the application you'd like to work with and then proceed to Server -> Manage Crons:  

You will see the cron job management panel:

Here, you'll be able to add a new cron job. We start off with the intervals - by default, the interval is one hour ( 0 ), but you can adjust it as needed. To run a command every ten minutes, you need to fill out the fields like this:

and to run it every two days:

or every day at 10 AM EST:

The command field is the most critical part - you will most likely be provided with a command, or URL that needs to be placed there. If you have an URL pointing to a file on your site, you should use either WGET or CURL in order to call that file and run it via a cron job:

curl --silent 'http://mywebsite.cloudaccess.host/index.php?option=com_somecomponent&task=runalltasks'

If the cron job requires a physical path to a PHP file, PHP should be used and the call would look like this -

php /mnt/data/vhosts/casite-xxxxxx.cloudaccess.net/httpdocs/folder/housing/the/file/file.php

The casite-xxxxxx part needs to be filled with the numbers from your document root path, which you can find under Server -> Overview in the CCP for your site.
If you are not sure how to add it (or how to prepare the command you have, you can always submit a support ticket and we will help you out.