The plot request plots Calls on the vertical axis and Date on the horizontal axis. HAXIS= uses a monthly time for the horizontal axis. The notation '1JAN94'd is a date constant. The value '1JAN95'd ensures that the axis will have enough room for observations from December. 
proc plot data=emergency_calls;
   plot calls*date / haxis='1JAN94'd to '1JAN95'd by month;