What is philosophy, and what are the main features of this concept

Philosophy is the study of knowledge. It can be about the investigation of nature, principles of reality, questions about existence, and the nature of man (and many more!)

I'm not sure of any exact features.

Questions tend to be about what is and what should be. They tend to be about ethics, metaphysics, and epistemology (what can we know and how)

Philosophical questions are also important, they have a purpose.