Extruder does not extrude plastic

This can have two reasons:
 
(1) The nozzle is clogged 
Solution 1Clearing a Filament Clog or Breakage (without removing extruder head)
Solution 2Manually cleaning and refurbishing the extruder head
 
(2) The nozzle height is too close to the turntable
SolutionAdjust nozzle height