We want to make our own themes with designated background, theme color and logos. To add a theme, what we need to do is to create a package for this theme. Copy the existing theme from drupal/modules to drupal/sites/all/themes/

The folder containing the theme should match the name for the .info file inside the package. Modify the first line of the info file for NAME field to whatever human-readable name you call it.

After that, you'll see the new theme in Home/Administer/Site building/Themes/.