To use WadC, you require Java, a Doom engine, a node builder and game data for a Doom game (known as the IWAD).

WadC is packaged for Debian and Ubuntu-based distributions. You can skip all of these steps, simply do swirl Ubuntu 
$ sudo apt install wadc
$ wadc
  1. Pre-requisites
    1. Java
      1. Linux
      2. Mac OS or Windows
    2. Doom Engine
    3. Node Builder
    4. Game Data (IWAD)
  2. Configuring WadC
      1. Mac OS
  3. First run

Pre-requisites

Java

WadC requires a Java Runtime Environment to run, version 8 or newer.

Linux

On a Linux-based distribution, I recommend installing OpenJDK. For Debian-based systems

apt install openjdk-11-jre

On Fedora/Red Hat style systems

dnf install java-11-openjdk

Mac OS or Windows

Download and install AdoptOpenJDK's build of OpenJDK here.

Doom Engine

You'll also need a Doom engine. I recommend Crispy Doom (Debian package crispy-doom).

Node Builder

Finally you may require a node builder. I recommend zdBSP (Debian package zdbsp).

Game Data (IWAD)

IWAD (game data). If you don't have the commercial game data, buy it from GoG or grab FreeDoom (Debian package freedoom).

Configuring WadC

Unpack them all.

Launch WadC by double-clicking the JAR file.

Open WadC's preferences dialog (⌘ + ,) and set the paths to the game engine, IWAD and node builder (these should be set to sensible defaults already if you installed the Debian package).

Mac OS

Most Doom Engines for Mac OS are distributed as "app bundles": within the UI, they appear like applications that can be double-clicked, have an icon, etc.; but under the hood they are actually folders that contain other files (e.g. Eternity.app/). One of the included files is the actual engine program.

When selecting the game engine, WadC requires you to select the engine program from within the App bundle. The File chooser should let you expand the App as if it were a folder and browse the contents. For example, for Eternity, the engine is Eternity.app/Contents/MacOS/Eternity Engine.

First run

Open up one of the files from examples/ in the unpacked WadC ZIP. From the WadC Control menu, hit Run / Save / Save WAD / BSP / Doom to try it out!