If you arrange an event or meeting, you make plans for it to happen.

If you arrange with someone to do something, you make plans with them to do it.

If you arrange something for someone, you make it possible for them to have it or to do it.

If you arrange things somewhere, you place them in a particular position, usually in order to make them look attractive or tidy.

If a piece of music is arranged by someone, it is changed or adapted so that it is suitable for particular instruments or voices, or for a particular performance.