The following are some resources that have helped me as I try to figure out what it means to be a manager and a leader. This is not intended to be an exhaustive list, merely a jumping off point. A few items here may catch your eye right away, start with those ones, and follow them wherever they lead you.
Some of the resources below may not be obviously linked to management, in which case I probably included them because they helped me understand myself better. Being a manager or a leader requires an ability to understand others, but a precondition for understanding others is definitely understanding yourself.