The folder structure is the way you go to organize the Assets of your project, you only have to create a folder for each type of asset you’re gonna use in your project. To create a folder select the project window in Unity > Right click in the assets folder > Select “Create” > Select “Folder”.
This is an example of a base folder structure for a 2D game:
AnimationsAudio— — — — Music— — — — SFXFontsPrefabsScenesScriptsSprites
The folder structure will help you to find your assets easily and faster, this is not a mandatory step for every project and it can vary depending on the assets that you will need, for example if we create a 3D game we have to add folders like Models, Materials, Textures, etc.