I assume you want to play your song with Melodyne as a plugin on one track and hear the Melodyne corrections?
- Install Melodyne as an audio effect plugin.
- Insert an instance of it in the FX box in the Inspector for the track in question.
- With the Melodyne GUI open click 'Transfer'.
- Play the part of the track you want so it appears in Melodyne.
- Do your note corrections/manipulations.
- When you now play the song you wll hear the effect.
You can then bounce a 'corrected' clip/track/part of a track to a new track. I always keep the original track for safety and possible use for a double tracking effect.
Melodyne have lots of very helpful tutorial videos here:
http://www.celemony.com/cms/index.php?id=videos#top