This is a list of the most common files you'll edit when creating a mod. It is recommend that you download the tools to extract the game resources before continuing. That way, you can reference these files as you go.
.decl File Extension
.decl files (short for "declaration") are the most commonly used files in Doom Eternal modding. They are a form of script or "pseudo-code" that is interpreted by the game engine. Many of the variables and numeric values used by the game are defined in these files. They can be edited with a text editor.
> File to edit the Rocket Launcher.
.entities File Extension
The .entities file contains all of the data in a map/level except geometry — if you want to make a level mod, you will need to learn how to edit the .entities file. These files are stored compressed, and require a tool to decompress them. After that, the file can be edited with a text editor.
> Level file path for Hell on Earth.
.tga File Extension
These are texture files. If you want to create custom skins or other artwork, you will most likely be editing these .tga files. Not everything "visual" is a .tga file. Many of the game's particle effects, lighting effects, and other visual effects are controlled by .decl files instead.
Texture editing software is required to edit .tga files.
<resource>/models and <resource>/art
> Texture files for the Arachnotron's model.
Despite the name, the ".tga" files used in Doom Eternal are not actually .tga (targa) images. You will need to use a tool such as SAMUEL or VEGA to extract them in a usable format (.dds, .png, or .tiff).