psychology
Psychologie is used in French in the same way as psychology is used in English. It refers to the scientific study of the human mind and its functions, especially those affecting behavior in a given context. You would use it when talking about mental processes and behavior, or the profession of studying and applying understanding of the mind.
Psychology is a fascinating discipline.
This is a simple declarative sentence presenting 'psychology' as a subject, and expressing an opinion about it.
I'm going to study psychology at the university.
In this sentence, 'psychology' is the object of the action 'study'. The speaker is telling us about their future plans for study.
My psychology professor is very competent.
In this example, 'psychology' is used as an adjective to describe what type of professor the speaker is talking about.