You can select the draw (pencil) tool (next to the arrow tool or by pressing D) and click on a note and it will play it (you'll want to make sure the pencil turns into an up/down arrow instead of sideways arrow). If you accidentally click on a note or want a reference pitch, you can click on the note and hit the delete key on your computer keyboard, and zap - it's gone. This is a quick way to audition notes you may or may not want to use. You can also drag notes up/down/left/right.