Right click King Arthur's Gold in your Steam library, click "Properties", select the "Local Files" tab and click "Browse Local Files"
OR
Go to your Steam installation folder -> steamapps -> common -> King Arthur's Gold

Open autoconfig.cfg and change variables. Here is a table of useful ones:

Don't forget to port forward port 50301 (or your custom on if you changed it) UDP!

Execute dedicatedserver.bat/.sh and press Play to run the server. It takes a minute for it to run, it's ready when it says something along the lines of "SERVER EMPTY - GAME PAUSED".

Open up your game and either fill in 127.0.0.1:50301 (replace 50301 with a different port if you changed it) in the "Connect To" tab or join via the server browser. Others should be able to join via the server browser.

Open the Security folder and remove the .example extension from all(!) the files. Open up superadmin.cfg and add your name ending with a semicolon like this:
Note that this is not your steam nickname or username, but your KAG username. If you don't know what it is, join a server or solo game and look on the scoreboard in the "Username" row.
I don't recommend you to make anyone other than you yourself superadmin. If you wish to add admins open up admin.cfg and add names just like before seperated by a semicolon:

I will not be going over making mods or fixing them, but if you have a working mod you open the Mods folder and paste all the mod's contents in a folder with that mod's name. After that open mods.cfg in your main King Arthur's Gold folder and write the name of the mod (folder) there.
Images for simplification:
My mods folder with the mod "CoolMod" I want to use: http://i.imgur.com/Ke0qEVi.png
My mods.cfg: http://i.imgur.com/6FrR1YL.png


You can download mods on the official forum's resources section: https://forum.thd.vg/resources/
For further assistance ask the on official forum's help section: https://forum.thd.vg/forums/help.81/ (preferably - but here is also allowed obviously)

Cheers