php - crontab - how to create in Terminal?

I'm trying to run a scheduled task on my shared Linux server using the crontab via Terminal on my Mac.

I can login to my ssh OK, and can view directories etc with ease.

I try and create/edit my crontab by using...

crontab -e

But i get the response

no crontab for [username] - using an empty one

So trying to then add my line to set my schedule up, and Terminal just doesn't seem to respond.

10 * * * * /home/username/www/myphpfile.php

Any clues what on earth I'm doing wrong? Or a link to a clear step-by-step tutorial?

I have checked with the webhost that this is supported, it's just undocumented!

All I want to do is run a php script every so often through the day (to check for updates to an XML file).