Those sliders let you zoom in and out, as well as scroll on the piece. They function almost like regular sliders, except that the thumb handles can be moved to control the zoom level.
To zoom in either vertically or horizontaly, simply grab a thumb handle (the arrow button at the side of each slider, marked as (1) and drag it towards the center. As you drag, you see a smaller portion of the view, enlarged.
Once you have zoomed in at a desired level, you may scroll the view, either by selecting the center part of the slider (2) and dragging it, or by clicking in the outside parts of the sliders (outside the area surrounded by arrows, marked above as (3).
To reset the view to see the full piece, you may click in the lower right corner button (4).