Management involves coordinating and overseeing the work of others to achieve organizational goals efficiently and effectively. There are three levels of managers - first-line managers who oversee non-managerial employees, middle managers who oversee first-line managers, and top managers who make high-level organization-wide decisions. Managers perform four core functions - planning, organizing, leading, and controlling. They also take on roles such as leader, liaison, and monitor. To be effective, managers must have technical, human, and conceptual skills. Both the internal environment of an organization and external factors in its task and general environments influence management.