OnSong allows you to write songs with simple text and then do amazing things like transpose on-the-fly. Flow is a powerful feature that allows you to arrange the parts of your song to match how it will be played.
In this tutorial video, Jason reviews what flow is and how to write your songs into sections. He then covers writing the flow of the song in abbreviated and long form as well as how to output notes and pages using the flow tag. Last, he'll cover a featured called Separate Set/Song Styles that lets you setup the style, key and flow of a song differently in a set than in your main library.