Mods have a pre-arranged file structure that they must adhere to. Basically we as the developer are showing the engine where to look for game resources, be it sound effects, textures, landscapes, or models.
-Navitgate to your mod folder, in our case it will be the myfirstmod folder -Double-Click to enter the folder -Right-Click and select "New Folder" -Rename the folder "data" without the quotations
(Note: This stage is required for any mod, and must be set up like so for the mod to be recognized by the game engine.)
So far your setup should look similar to this depending on your operating system. Below is an example using windows seven: