Using drush to install multiple sites, how?
If you want to use 1 DB for multiple sites you should get https://www.drupal.org/project/domain. I haven't tried it yet, looks complicated to set up, so good luck =) 

For pointing your site, this video might help, skip to 15:49 http://www.youtube.com/watch?v=Ea_Tqd-NrC4 It doesn't cover diff root directories for diff domains tho.