No single multisite setup method above got me all the way there; if you have cPanel and Drupal installed on your original domain, follow these straightforward instructions to set up a multisite:
For 'www.yourlovelysite.com':
1. in cPanel, go to 'Subdomains'
2. enter a name for you subdomain; this is followed by '.' and your original domain name automatically, e.g. 'sub1' becomes 'sub1.yourlovelysite.com'.