This is a standard Unity project, with one important exception. 

The content for the game comes from a JSON file and the logic for deserializing the file and working with the data is entirely external to Unity, in the DataImport solution. That should be opened separately in Visual Studio. When changes there are ready to be used in Unity, you'll need to build the solution, go to the output directory, copy the DLL's for DataImport and FullSerializer-Unity, and paste them into the Assets/Libraries directory of the Unity project. After that, you should be all set to continue working in Unity as usual.