Here are the instructions. Not sure what part you don't understand.
I have added hints in blue.
The base PRR model is required.
To install this engine, use the TS Utility to install the RWP file.
This is utilities.exe which is in the Railworks program folder.
Easier still:
1- Find your Railworks program folder in Windows explorer and leave the explorer window open;
2- Open GE44Tonner-NERW.rwp with 7zip;
3- Drag the Assets folder from 7zip to your Railworks folder. Accept when prompted.
Copy ..\Assets\DTM\GE 44 Ton\RailVehicles\Pennsylvania\Engine\GE 44Ton_Penn.GeoPcDx to
..\Assets\DTM\GE44Ton-NERW\RailVehicles\NERW\Engine\
Copy ..\Assets\DTM\GE 44 Ton\RailVehicles\Pennsylvania\CabView\GE 44Ton_Penn_Cab.GeoPcDx
to ..\Assets\DTM\GE44Ton-NERW\RailVehicles\NERW\CabView\