Understanding the Publishing Portal - Azure/AzureTestDrive GitHub Wiki
Publishing Portal
The Microsoft Publishing Portal is where Publishers come to create and sell their marketplace offers. To build a Test Drive you must first publish an offer on this Publishing Portal.
https://github.com/Azure/AzureTestDrive/blob/master/AzureTestDriveImages/pubportal1.png
[Note: If you do not have access to the Publishing Portal it might mean you have not registered with Microsoft to become a Publisher! Please read and apply here.]
For more reading about Marketplace Publishing, the general documentation is here.