Arrangements allow you to create multiple layouts for a song without having to duplicate the song in your Library. After you have built your arrangements, you can then select which version of the song you want used.
Every document has a Master arrangement that contains all of the slides in your presentations. Arrangements contain a sub-set of the slides in the order you set them. Generally, the version shown in the Library will be the Master version. You can change the default version shown by right-clicking on the song title and selecting an arrangement from the Arrangement list.
You can also change the arrangement being used by selecting it from the Arrangement Editor at the tp of the presentation. This option can be used to set the arrangement in the Library or when you have the song in a Playlist
The final place to select the arrangement is from within the Playlist. Right-clicking on the song will give you the option to select the arrangement similar to selecting it in the Library. You can have multiple versions of a song in any playlist, just select the arrangement you want to use for each version.
When you are viewing a presentation that has an arrangement other than Master selected, it will be indicated next to the title at the top of the presentation.