Use the Track Sheet to change the play/mute/solo status of each track.
Each track will play if there is a circle in the Play field. It will be mute if there is no circle. Click on the Play field to remove or display the circle.
Click on a track's Solo field to solo that track. A circle will appear in that field and now only that track will play when you play or record. Click on the Solo field for another track and the new track will become the solo track. Revoke the solo status of a track by clicking on the circle in the Solo field. The circle disappears and no track has solo status.