Think of the tracks in your Timeline as the different musicians in your band. Each musician plays a different instrument and is represented by a separate track. As the leader of your band, you can decide which instruments are used in a song and how you want to record them. If you don't like an instrument part, you can always fire the musicianor in this case, just delete the track. If you really like the way a part sounds, you can clone the musician, or just double that track in the Timeline.
The best way to understand tracks is to work with them, so let's get started.