According to Mental Health.org, mental health includes our emotional, psychological, and social well-being. It affects how we think, feel, and act. It also helps determine how we handle stress, relate to others, and make choices. Mental health is important at every stage of life, from childhood and adolescence through adulthood. Over the course of your life, if you experience mental health problems, your thinking, mood, and behavior could be affected.
I hope this helped you understand what mental health is.