Ok I'll try.... composition in a nutshell, is the way you design an image. You include something, you exclude something. The way you design an image will depend on what kind of message you want to convey, a scene you wish to show, a comment you'd like to make, something you want to document or just something/some place/someone you want a memory of, etc, etc, etc. Composition is something that helps the images you take stay relevant to your thoughts. So there you have it..... function of composition. Which comes first, you decide.
I think composition depend on type of photography
-Abstracts and Still Life
-Land/City-scapes and Travel
-Macros and Close-ups
-Reportage and Sports
-Portraits and Poses
-Ready, Lights, Action!
-Street and Candids
-World of Nature
The first function of composition is to edit the image. To show people what you want them to see, to exclude what you don't want them to see, and to arrange what you want them to see in a way that you want.
This is not much different from what news editors (and the film censors) do on a daily basis.