You've been directed here because the project you're viewing uses Protobuild to generate it's projects.
If you are on Windows, you can quickly generating projects for the default platforms by double-clicking on the Protobuild executable in the root of the repository.
If you are on Mac OS X or Linux, you'll need to open a terminal, and once in the root of project repository, run:
$ mono Protobuild.exe --generate
You'll need Mono installed if you are on Mac OS X or Linux.
If you want to use Protobuild for your own projects, and potentially use this project as a submodule, refer to the :ref:`user-docs`.