In general, composing and arranging are both important parts of music creation, but they have different tasks in the creative process. The composer is mainly responsible for arranging the lyrics, while the arranger is responsible for expanding the expression of the music without affecting the main melody and content of the original song.

1. Composing music: The process of composing music is mainly to set the lyrics to music. Musicians express the creator's musical ideas through the use of professional technical theoretical systems such as harmony, polyphony, orchestration, and musical structure. Composition is usually completed by lyrics and music, but sometimes the music is composed first and then the lyrics are written.

2. Arranging: Arranging refers to accompaniment for a single melody, which expands the expression of the music without affecting the main melody and content of the original song. In classical music, the concept of arrangement did not originally exist, because all composers wrote their own scores and stipulated the coordination of all instruments. But as time went by, the concept of arrangement came into being, which allowed for more exploration and experimentation in the expression of music.

To sum up, the composer is mainly responsible for arranging the lyrics, while the arranger is to expand the expression of the music without affecting the main melody and content of the original song. These two links are indispensable in music creation, and they completed a musical work together.