If you hit the spacebar your track will begin to play back and, if you're feeling adventurous, you can select your track and press Shift+Command+K to bring up a software keyboard and play along.
Pan adjusts the balance of the instrument to the left and right of your mix and the volume control is self-explanatory. Muting, as you would expect, silences a track, while solo mutes all other tracks.
Each instrument has basic adjustments available, such as Mute and Solo controls as well as volume and pan settings.
