Selecting the Synchronize with your iTunes music library radio button and clicking Next opens another window that allows you to set the location of your iTunes music library XML file, your primary music library.
Use this method if you are an iTunes user. SuperSync should find the location of your iTunes library (and the XML file it generates) but if it doesn't, you can set the location manually.
The iTunes XML file is the data file that updates your iTunes library listing and is automatically created and kept up to date by iTunes.
If SuperSync can't find your iTunes library, click Set under iTunes Music Library XML File to select this directory. It is usually located in your computer's Music folder or Documents folder.