Compositing is a very interesting subject in creativity. It involves every area of art in every form depending on what exactly is to be done.
Compose pictures with pictures to form a picture, pictures with pictures or movies to form a movie, nature and drawing to form a design and the list goes on.
The above picture is a composition of a lot of pictures and the youtube video is a composition of drawings and text and movies to form a movie.
To learn more see me on youtube for video tutorials.
You can compose a full video such as this for any situation using images and drawings to achieve your animation movies