This is the Direct CD Access window. From here you can control current disc and track playing position.
There are two sliders in this window: one for entire disc access and one for current track access.
Click on the gizmo on the image below you want to learn more about:
A slider can work in one of three slider modes: track labels (disc slider only), time and percentage. In track labels mode you can quickly seek to the desired track by clicking on track label ('1', '2', '3' ...). You can switch between slider modes simply by clicking on the text label at the top-right corner of slider.
See also: