The portals are compatible with the Online and On-Premise version 8.1 and later. The important thing to note is that this source code is provided to customers that are unable to deploy portals in an online environment, and are willing to maintain the portals code internally. Microsoft is not planning on supporting this code, which is also why it is provided under the open source license, and at the point of writing this, there are not acknowledgements of whether or not this will be supported in the future.
The download contains the solution files, the source code and the deployment instructions of the source code. The integration with the Portals web application can be implemented using a internal/organizational IIS server or using Microsoft Azure.
You can download the portals from the following link: