How do keys work in music and how do they influence the overall sound of a musical piece?

Keys in music refer to a set of notes that create a specific tonal center for a piece of music. They influence the overall sound by establishing the mood and emotional quality of the music. The key determines which notes are used most frequently and creates a sense of stability or tension. Changing keys can alter the feeling of a piece, making it sound brighter, darker, happier, or sadder.