When you open a surface, it appears with no toolbars or icons visible on the screen. The image is actual size-one inch on the surface = one inch on the monitor. This is called Full Screen mode.
When you move the mouse, a control toolbar and thumbnail panel appear at the bottom of the screen. When the mouse is still, the toolbar and panel disappear.
Tip: You can set the control toolbar and thumbnail panel to be always visible on the screen–see Setting Preferences.