All the essential controls for drawing, editing, and playback are located on the bottom of the screen.
These are the Undo and Redo buttons.
This is the Play button.
Playback begins from the red line going down the center of the screen.
This is the Rewind button.
Whenever you hit the Play button, you automatically create a new rewind point. After this happens, you'll go back to the last playback position whenever you rewind.
This is the Record button.
If you tap this button, your composition will start to play and you'll be able to draw notes from the play line without having to hold down the canvas. Hit the Record button again to stop.
This is the Erase button.
Erase works just like drawing. Once you tap the Erase button, you'll be in Erase mode. To go back to Draw mode, tap the Erase button again.
One small hidden feature: if you hold down the Play button, a radial menu will appear that lets you modify your playback speed!