The DSM-5 is a manual used by mental health professionals to diagnose mental disorders, organized into categories based on symptoms and criteria. It introduces the concepts of spectrum and dimensionality, which recognize that mental health conditions exist along a continuum rather than as distinct categories. Social workers and mental health professionals use diagnoses to guide treatment, though there are concerns about overdiagnosis and the importance of distinguishing between grief and depression, particularly in cases like a teenager coping with the loss of a friend.