The gridding editor is still in a very early development stage. There will be more documentation as soon as the main functionality is stable.
Usable functions are:
Loading files (Open File)
Saving files (Save, Save as)
Moving grids: Klick 'Move Grids' button and klick on a grid once. It will stick to the mouse until you click again.
Zooming/Scrolling the display: Use the sliders on the image display area edges.