Background music, background sound, etc., into their respective folders.
The 'audio' folder is where you will place audio. Faces, battlers, etc., into their respective folders. The 'img' folder is where you will place all graphics from the DLC. Inside you will find, amongst other things, a folder called 'img', one named 'audio', as well as one named 'js'. The standard folder is Documents\Games\insert-your-project-name-here. This is not necessarily the case with custom resources that you made yourself. The resources inside steamapps\common\RPG Maker MV\dlc\BaseResource\img goes inside the 'img' folder of your project. With the DLC, the resources usually come with sorted and in folders that correspond to where they belong in your project's folders.