His whole thread, especially the first post, is a tutorial of the technique(s) you can use with that. It is only for Stock, and is not 100% fully functional, as he states, but has enough to keep most folks entertained for hours on end. You'll want to get
JSGME to facilitate your adventure. You place the JSGME file in the "root" game folder (default of "Silent Hunter 4: Wolves of the Pacific") and run it it will create a "MODS" folder, which is were you will place any mods you go to apply to the game. If you need to,
7Zip is a good archive utility that won't give you the extra folder than can resulf from using the Windows archive manager. If you do use the Window archive manager, just make sure your folder structure doesn't have a repeat folder in it, such as "MODS / ModName / ModName / Data", or similar. You should also run the JSGME "Tasks - Generate snapshot of game files" before doing any mods. It will take it a few minutes to run. You can use the snapshot to find any future issues.