Congratulations on deciding to be an advanced maker of maps.
Before you start, make sure the mod you downloaded works properly. To test it:

Place the mod in the right folder:
• Go to your Documents folder, then locate a folder called Command and Conquer Tiberian Wars . Inside this folder, create a sub folder named mods (if it doesn't already exist).
  
• This is where your mod should go.
  
  Create a subfolder for your mod:
  
• Inside the mods folder, create another subfolder with the name of your mod. For this tutorial, we’ll use "exnoforce" as an example. Extract your downloaded mod into this folder.
  
  Test the mod in-game:
  
• Launch the game with the ui screen to ensure the mod appears in the browser and runs correctly.
  
• If you need help getting the mod selection screen up there is already a great tutorial on steam here

Now that the mod is working, follow these steps to add it to the WorldBuilder:

Locate WorldBuilder's directory:

• Find the folder where WorldBuilder is installed. You may need to search for the worldbuilder.cfg file to locate it.

Copy the required files:

• Copy the mod.big and mod.skuldef files from your mod folder (e.g., "exnoforce.big") into the WorldBuilder.cfg directory.

Next, you need to update the worldbuilder.cfg file:

Make a backup first:
• Open worldbuilder.cfg in Notepad. Before making any changes, save a copy of the file as backupconfig.cfg. This ensures you can always return to the original settings if needed.

Add your mod's file to the configuration:
• At the bottom of worldbuilder.cfg, add the following line:
  
• try-add-config "exno.skuldef" (Replace "exno" with your mod’s name if different.)

Save and close:
• Save the file as worldbuilder.cfg
  
• Your done and now can open the worldbuilder by double clicking the crystal application icon

Out of memory errors can occur when loading bigger mods if you are running worldbuilder on max settings I strongly urge you to set the LOD setting in the editor to low when making maps for big mods , and to create as much as possible with the standard worldbuilder Before you edit it again with your mod added to it. Use multiple copies of your map so that autosave does not ovewrite it.
Do note when maps are loaded in the game they will look great even if you made it in lod low mode.