To set up your server, make your way to wherever the program is installed, normally its in "Steam/steamapps/common/Knockout City - Private Server Edition", go to it and open KnockoutCityServer and run the .exe, as long as its running you'll be able to connect to it and play.

This is the more tricky part of the tutorial, as you'll need to do a lot more.
First, create a new shortcut on your home screen, and link it to the normal game, not the server.
Then you will need to add a launch command to the end like this:
("path\KnockoutCity.exe" -backend=1.1.1.1:20000) remove the parenthesis.
To get it to work, you will need to change the fake IP to your desired servers IP, in the servers cmd window, it should display 2 IP addresses, one for local, and one for external. If you are playing on the same WiFi as the one with the server, use the Local, if you are on a different WiFi then the host, you need to use the external, the IP will have an extra period at the end you will need to remove.
(1.2.3.4. = 1.2.3.4) You will also need a port to host it on, try hosting it on something above 20000 like shown above, as these are normally safe to use.

You can also add the Launch Command through Steam, by going to the games properties and adding "-backend=1.1.1.1:20000"

All you need to do now is to save the shortcut and run it! Now you and your friends will be able to play. (Matchmaking will not connect to other peoples servers, only people running on the current server, so make sure you have enough friends for the game mode you are trying to play.)