Managers perform key functions like planning, organizing, staffing, directing, and controlling. They take on interpersonal, informational, and decisional roles. Managers need strong interpersonal, technical, and decision-making skills to effectively and efficiently use resources like human, financial, physical, and information to achieve objectives. Managers operate at three levels - top managers oversee the entire organization, middle managers implement strategies, and first-line managers supervise employees and implement plans.