Setting Cron for RSS Feeds

[Jacksplat]

I've searched here all week, I give up and hope someone can tell me what I need to know or direct me to a thread that's discussed this before.

I have RSS Feeds on my forum, I update them manually in the update feeds 3 times a day. I know I can put this in a cron job but have never messed with cron before. There is a cron option in my cpanel and there is a cron job in my vbulletin admin panel. I need to know which of these I should use, and what would the command be in either. An example of the command would rock. The example can contain any url for the feed, I can replace it with my own.

Thanks in advance.

Jack