Philosophy (from Greek φιλοσοφία, philosophia, means literally "love of wisdom").
Since  the beginning of mankind ,  people seek to understand fundamental truths about themselves, the world in which they live, and their relationships to the world and to each other. 

Important parts are:

-Metaphysics

-Epistemology

-Ethics

-Logic

-History of Philosophy

The study of philosophy involves not only forming everybody's own personal answers to such fundamental questions, but also to understand how people in the past have answered such questions of the human nature,  as there would be for example

Plato  | Locke  | Marx| Aristotle  | Hume  | Mill | Aquinas  | Kant  | Wittgenstein | Descartes  | Nietzsche  | Sartre | de Spinoza