Cron jobs are programs that allow users to schedule scripts to automatically run at a set date / time.

From the Cron Jobs (Admin Interface -> Settings -> Site Settings -> Cron Jobs) menu, select to:

Run cron jobs from the server's control panel

Add ONE of the following lines and set it to run, if possible, every minute:
curl -s http://www.yoursite.com/cron.php
wget -q http://www.yoursite.com/cron.php

Important: Add a cron job with one of the commands below to purge unused images - the cron job should run once per hour:
curl -s http://www.yoursite.com/cron.php?command=purge-unused-uploaded-files 2>&1
wget -q http://www.yoursite.com/cron.php?command=purge-unused-uploaded-files

Optional Feature: Add a cron job with one of the commands below to update the currency exchange rates - the cron job should run daily:
curl -s http://www.yoursite.com/cron.php?command=update-currency-exchange-rates 2>&1
wget -q http://www.yoursite.com/cron.php?command=update-currency-exchange-rates

Run cron jobs from within the application

Cron jobs will be run automatically each time the site is accessed. To be used only if the user doesn't have access to the cron tab application on the server.