Flow is a feature that allows the basic components of a song (verses, choruses, bridges and more) to be arranged in a particular order. OnSong then displays those parts of the song to create one continuous page. This allows the song to be experienced in a linear fashion by scrolling from the top down.
The system is very flexible and requires you only to label the sections of your song. You can then use an abbreviated version of the flow, or a more verbose version to allow even more options like displaying musical instructions at just the right time in the song.