You can both navigate and zoom image using one of the options.
Arm (A) and Zoom tool (Z) is located on the Toolbar right above Pen tools.
To Zoom In hover the pointer over the image in Editor or Result and move to the left holding the mouse button down or press (CTRL++/Command++)
To zoom out press the mouse-button and move the pointer to the right or press (CTRL+-/Command+-)
Navigator enables you to (a) zoom, (b) navigate the image, (c) switch between Editor and Result, (d) enable/disable Scale Synchronization between views.