Mentors are different to your manager and different to a coach. Managers and coaches help answer or find answers to your questions, as well as help you do your job.
A mentor is someone you turn to for longer-term advice and to see the bigger picture … or maybe the same picture from a different angle! They have less of a vested interest in you thank your direct manager and might therefore be more objective. That doesn’t mean they don’t care. In fact, it is quite the opposite. They have your longer-term best interests in mind. For these reasons they are highly valuable to help you transition into a professional career and develop your career long term.