Arranging and composing are two different processes in music. Arranging is the process of taking an existing piece of music and reworking it to fit a different style or instrumentation. This can involve changing the melody, harmony, rhythm, or orchestration of the original piece. Composing, on the other hand, is the process of creating new music from scratch. This can involve writing new melodies, harmonies, and rhythms, as well as creating a structure for the piece. Arranging is often done for specific performances or recordings, while composing is typically done for the purpose of creating new music. Both processes require a deep understanding of music theory and composition techniques, as well as a strong sense of creativity and musicality. In short, arranging is about taking existing music and making it your own, while composing is about creating something entirely new.