This area shows which part of the sound is currently selected (Selected area) and which part of the sound is displayed (Displayed area) by the wav form area. The selected area is shown as the green rectangular area, and the displayed area is shown by red lines. The non-selected area is shown as navy blue.
When you click left button of mouse in the displayed area, that point is considered as the start time of selected area. With the right button, it is considered as the end time.
These operations are same as wav form, but in the selected area you can set them from start of wav file to end time of it. You can set them only in displayed area at wav form.