Here's a description of the tool taken from Codeplex:
The release of the Virtual Machine Role in Windows Azure Pack and System Center 2012 R2 introduces a cloud service application deployment model to deploy virtual machine workloads that will be deployable on premise and in Windows Azure in the coming year.
Hand-crafting these packages against the published schemas of the model is a slow and tedious task.
If you want to see this tool in action, then I highly recommend you check out this series of tutorials from Microsoft's Charles Joy here:
Creating a Linux VM Role Resource Definition
Creating a Linux VM Role Resource Extension
Creating a Windows Server VM Role Resource Definition
Creating a Windows Server VM Role Resource Extension
Updating a Virtual Machine Role Gallery Item
When you've watched the video's, I'd recommend that if you're interested in WAP and System Center 2012 R2, then you subscribe to Charles' YouTube channel (http://www.youtube.com/user/charlesjoyMS) to keep up to date with anything new he releases.