The configuration.php file for Joomla has paths and URL's for your site which will need to be changed when you move the site into production.
If you're already running Joomla, or some other production site, your dev Joomla installation will need its own database, hence joom2_db and its associated user.
One-Click keeps track of the installation directory and database associated with the installation. One-Click will only upgrade the Joomla that's in the original directory, and the original database.
To move an installation from a test environment/URL to your production environment/URL if you plan on sticking with One-Click upgrades, you'll have to do the following:
0) Back everything up! (Joomla directories and databases)
1) Your existing site must have been installed via One-Click, or you'll have to do a trial One-Click to your production site.
2) Move/Copy your test Joomla directory (dev.yourdomain.com) to your final directory (yourdomain.com).
3) Drop all tables from your production database (the database created with the One-Click to your live site). Restore your dev database into your production database.
4) Edit the configuration.php file with all the proper settings for your production site.
If this is a lot of confusing hoops to jump through, you've got a few choices:
a) Bone up on UNIX and MySQL.
b) Find someone who is up on UNIX and MySQL.
c) Give up on One-Click support, which would require that you do manual Joomla upgrades, sending you back to a) or b).