What is a cronjob:
The software utility cron is a time-based job scheduler in Unix-like computer operating systems. People who set up and maintain software environments use cron to schedule jobs to run periodically at fixed times, dates, or intervals. ...
Does your hosting provider give you access to CPanel or any other hosting management tool? If you have CPanel -> you need to go to the cron jobs section and setup the cronjob.
Then in the field for the cronjob you need to type:
/bin/wget -O /dev/null "http://yoursite.com/index.php?option=com_comment&task=queue.cron&format=raw&total=10"
You need to aks your hosting provider what the path to wget is. Wget is a computer program that retrieves content from web server/ basically a browser for the console.
For example on a siteground server as far as I can see the path to wget is /usr/bin/wget
if you want to send 100 emails when the cron is run just change total=10 to total=100
Cheers,
Daniel