GOG saves are usually located in %USERPROFILE%\Documents\Northgard .
As a GOG release, the game is pre-activated. Simply install and play. Northgard.v2.8.31.26467-GOG.torrent
If the content is compressed, extract the folder to your preferred directory. Northgard.v2.8.31.26467-GOG.torrent
Note that GOG versions typically use GOG Galaxy for multiplayer. If playing offline, "Local" or "Direct IP" options may vary based on your network setup. Troubleshooting: Northgard.v2.8.31.26467-GOG.torrent