As relating to this phone, you will encounter this a lot (if you plan to customize your OS - mostly once it gets rooted). USB debugging is basically allowing you to customize your phones operating system once the phone is hooked up to the computer.
If you have a Windows operating system you will need to download the appropriate drivers to allow the phone to be recognized by the computer once debugging mode is enable. By doing so developer.android.com find the sdk package download. Once that is downloaded and installed, open it and download the usb driver from the list of addons (may have to check force downloads to update addons list).
