When a song is loaded, the panel on top shows a large orange waveform that maps the song from start to finish. This waveform viewer can help you identify different parts of the song at a glance. Underneath the chord strip is a smaller similar shaped waveform. This is the zoom and navigation window. This allows you to zoom in and scroll up and down the waveform with greater ease. This will become useful when making loop selections.
Zooming can be achieved in 2 ways; firstly you can use the 'zoom' buttons to the left of the chord strip. Secondly, you can use the mouse wheel anywhere on the zoom & navigation bar. On Mac OSX you can use a 2 finger drag on the trackpad to zoom in and out. When zoom is active, you will notice that a section is highlighted on the zoom & navigation bar. This highlighted section is the current view in the waveform viewer above. In order to navigate to a new section of the waveform when zoomed in, you simply drag the selection on the zoom & navigation bar.