In the right hand side window, the various types of groups of instruments appear. They are the groups that exist in this very track.

Lets check the components of one track:
You can have Bass, Guitars and Percussions (usually includes drums). Enter the Bass group, and you may find the artist produced 2 bass tracks. Enter the Guitars group, and you may have three sub-groups including acoustic guitars, distortion guitars and solo guitars for example. Lets enter all three of the subgroups, to see how many versions of each the artist has produced. Now, enter the percussions group to find one drums subgroup and a percussions track. That?s a whole lot of tracks, yes...
Those with the little lights on are the current active tracks.

How are the tracks components behaving?
The artist produced the music track including various versions (many tracks), that is why you see so many. Some are destined to work together, and others to work with a different set. Using the ?MX? button below the right hand window will allow you to switch between the versions the artist has included. Doing this while the groups and subgroups are open will show you exactly which tracks have switched on or off.

When can I or can?t switch the tracks on/off myself?
It is the artist who decides the construction of his music. So he/she has decided to let you, or not, adjust the volume of the tracks separately and to switch on/off the tracks. This can be different on every track.

Technically, you could be listening just to one acoustic guitar, or just to the piano, by switching the tracks off. You could be listening to all instruments altogether (could result in cacophony...). The quality of the render is what pushes artists to keep a certain control over what you hear. The extra that you get, is to find out all the other versions of the track the artist has been thinking of, those ?garage? versions that he/she may have scrapped, and would go forgotten in the cupboard.