The stage movement arrows move your field of view when you "click" them.
You can explore the entire x4 view with the x10 lens. The field of view available for the x40 lens is however limited. How do you find it? Use the x4 lens and move to the upper left corner of the image. You should be able to switch to the x10 and x40 lenses. You may shortcut and push the "Reload" button of your browser - reloading the simulation can be very fast if your browser preferences are set correctly. Immediately after the loading of the simulation it is always possible to switch from x4 to x10 and x40. Switching directly from the lowest (x4) to the highest magnification (x40) does no harm on a computer, but it is not good microscopy practice. The simulations will not allow it.
The buttons "fine" and "coarse" set the movements of the stage to fine steps and coarse steps. The default setting is fine. Use fine steps to center features of interest at x4 or x10 before you switch to the x10 or x40 lenses. If you don't, you may loose the feature from your field of view.