Gravity uses a simple Model-View-Controller (MVC) pattern with a REST API. The structure of Gravity Sever is a server.js file, with api files routing requests from the client to the various controllers.
Controllers are located inside the /controller directory, the following come as standard:
pushtokenController (Native & Power plans)
Models are located in the /model directory, and the following are included for you:
notification (Native & Power plan)
pushtoken (Native & Power plan)
Views will either be located inside the /client/src/views directory if you're using Gravity Web as your front-end client, or else in the /app/views directory inside your Gravity Native installation folder.