Extracting Resources

In order to create mods, you will need to have the game's resources extracted into the various files that can be edited.
Resources are divided by levels or general categories and they will appear as folders when extracted.

Extracting Tools:

SAMUEL Asset Extraction Tool by SamPT - Download - GitHub
Currently exports textures, .decls, and .entities files.

EternalResourceExtractor by PowerBall253 - Download - GitHub
CMD Syntax: EternalResourceExtractor.exe [path to .resources file] [out path] [options]

Make sure you have enough file space when extracting resources. It can be very large if you plan on extracting everything.

List of Resources:

gameresources: General Stuff (You would be looking through this the most)
e1m1_intro: Hell on Earth
e1m2_battle: Exultia
e1m3_cult: Cultist Base
e1m4_boss: Doom Hunter Base
e2m1_nest: Super Gore Nest
e2m2_base: ARC Complex
e2m3_core: Mars Core
e2m4_boss: Sentinel Prime
e3m1_slayer: Taras Nabad
e3m2_hell: Nekravol
e3m2_hell_b: Nekravol - Part II
e3m3_maykr: Urdak
e3m4_boss: Final Sin
e4m1_rig: UAC Atlantica Facility
e4m2_swamp: The Blood Swamps
e4m3_mcity: The Holt
e5m1_spear: The World Spear
e5m2_earth: Reclaimed Earth
e5m3_hell: Immora
e5m4_boss: The Dark Lord
hub: Fortress of Doom (Campaign Hub)
dlc_hub: ARC Carrier (from TAG1)
shell: Main Menu
pvp_bronco: BATTLEMODE Celestial
pvp_darkmetal: BATTLEMODE Corrosion
pvp_deathvalley: BATTLEMODE Penance
pvp_inferno: BATTLEMODE Tundra
pvp_laser: BATTLEMODE Forsaken
pvp_shrapnel: BATTLEMODE Torment
pvp_thunder: BATTLEMODE Armageddon
pvp_zap: BATTLEMODE Extraction
tutorial_sp: Slayer Tutorial
tutorial_demons: Demon Player Tutorial
tutorial_pvp_laser: BATTLEMODE Tutorial
warehouse: Skins
meta: Contains "container.mask" (You would never need to use this)

There are folders with "_patch_#" appended at the end and they contain overriding files for their parent folder.
The patch number does not always mean it has a high priority because DOOM Eternal often changes the priorities with each update.