In a new, clean Magento Community installation, you are provided with the following design packages and themes:
Depending on your needs, you could add additional custom design packages, or custom themes within the Magento design package:
If you're going to install a group of related themes, you should probably create a new design package
On the other hand, if you're only using one or two themes based on the feature of the Magento design package, you can install the themes within the Magento design package hierarchy
We like to make sure that whatever we customize can be "undone" if necessary. It's difficult for us to make changes to the core, installed files; we prefer to work on duplicate copies, preserving the originals in case we need to revert back. After re-installing Magento for the umpteenth time because we had altered too many core files, we learned this the hard way!
Your new theme hierarchy might now look like this:
If you decide to use...