Clear opening size refers to the clear passageway when the door is open, if the door is hinged then the width needs to also take account of ironmongery which may project into the opening such as a push bar.  Structural opening sizes refer to the sizes left in the wall prepared for the door to be fitted.  Frame sizes refer to the size of the frame which will be installed, usually this will allow a fixing tolerance inside the structural opening.  So to calculate the required structural opening size you should work back from the required clear opening sizes + frame sizes + fixing tolerances = structural opening.