Copy the UnifiedOpennessLibrary.dll to your project and add it to your references. Then you will be able to use it. You can find a demo project how to do this in this repository.
The UnifiedOpennessLibrary contains one class called "UnifiedOpennessConnector". It is a disposable object, so use the "using" declarative to make sure it is disposed (this will dispose the TIA Portal object internally).
After initializing the UnifiedOpennessLibrary, you may access the TIA Portal, its project or other useful information.
You will find all features in the dll documentation, just start coding!
The user can find help by passing this parameter to the exe: -h or --help