Most interactive control is performed with the mouse. By holding
down a particular button, and dragging the pointer around,
various camera motions can be obtained:

   Left button:  Revolve camera around view target

   Left button + Shift key:  Revolve view target around camera

   Middle button:  Translate camera left, right, up or down

   Right button:  Dolly in or out

The first and last motions are generally the most useful.
Should the camera become difficult to control at any point, it
may be re-initialized by selecting Camera -> Reset View.