This module will guide you through the contents of the vanilla game, so you know what stuff goes to where. Then, basing upon this knowledge, you may create mods that add new contents or modify existing contents (even from other mods, and the DLCs also!!! Is that awesome?) by putting your ideas into the correct corresponding place.
You must at least have some knowledge on the concept of file structure itself. For example, do you know the relationship between files and folders in your computer?
2. The File Formats