To zoom so all items are visible click the 
Zoom all button at the top of the pane.
To zoom in click the 
Zoom in button at the top of the pane.
To zoom out click the 
Zoom out button at the top of the pane.
If your device supports gestures, you can also use a 'pinch' gesture to zoom in and out.
Toggle the 
button on/off to magnify the area under the mouse cursor. Magnification allows you to read a large plan without having to zoom in and out.
You can pan from side to side while zoomed in by left-clicking on the 
Floor Plan pane background and dragging it.
You can also zoom and pan using the wheel on your mouse (if you have one) depending on the Floor/Table Plan pane mouse wheel behaviour settings in the 
Preferences window.