I am working on a written final project and confused on how to apply psychological theories, processes, and concepts to human behavior. When it a person is believed to be suffering from major depression and then I am to

Discuss psychological disorders and treatment approaches of someone believed to suffer from major depression.
As I am working on my paper I am confused if would be appropriate to go over all the psychological theories or should I only go over major depression

I would go over depression, major and otherwise.