This is the Assets folder, required by Unity. All files and folders in this project shows up in the Project Pane.
This folder contains the following folders:
Scenes: Where all the scenes are stored.
Prefabs: Where all the prefabs are stored.
Models: Where all the 3D assets, especially models are stored
Models/Animations: Where all the animations are stored
Models/Textures: Where all the images specifically used for texturing 3D models are stored. Putting textures here makes it easier for the auto-generated materials to find its corresponding textures.
Models/Materials: Where all the materials used in models are used. Auto-generated material are created here.
Images: Where all the image assets used in a 2D context (such as particles) are stored. If an image is not used in a model, it goes here!
Images/GUI: Where all the image assets used in GUI are stored.
Sounds: Where all audio and sound effects are stored.
Sounds/Music: Where music are stored, especially background music.
Sounds/Voices: Where voices acting are stored.
Resources: A Unity folder where any file is accessible from script as if going through a normal filesystem. WARNING: loading assets from this folder is sloooooooooow!
Standard Assets: A Unity folder where imported assets are usually placed. Scripts in this folder are compiled first, allowing Javascript codes in the Scripts folder to access C# code.
Plugins: A Unity folder where plugins are installed.
Shaders: Where shader scripts are stored.
Scripts: Where the rest of the scripts are stored.
Scripts/Editor: A Unity folder where scripts extending any UnityEditor are placed in to compile. Basically, any script adding or changing a menu goes here.
Scripts/Gizmos: A Unity folder where scripts with OnDrawGizmos() function is defined. Basically, any script drawing debug symbols in the Editor pane goes here.