I just installed the Plugin but I have no audio

There are two parts to installing a plugin.
1. Importing the list of songs, their data and the charts.
2. Copying the contents of the "Materials" folder on the DVD into the RealBook Software's materials folder on your hard drive.

The most likely issue here is that you did not complete step 2.
Go back and copy those files into the "Materials" folder and that should resolve your issue.