This lists all the tracks for the current score.
To open the Track Properties window click on the Name of the track.
To open the Instrument Properies window, click on the Instrument column.
The "S" stands for solo, clicking on this will make only the selected track play during playback.
The "M" stands for mute, to mute the selected track during playback.
The volume and pan sliders adjust the volume and left to right panning of the selected track
Discuss this tutorial here