Concept translation: the Dutch text prevails.
Instructors teach you first to make sure nothing can roll: the trailer on its handbrake (handrem), the car too. Then you put the coupling (koppeling) on the ball (kogel) and check that it is locked, before you see to the breakaway cable (losbreekkabel), the plug (stekker) and the jockey wheel (neuswiel). Last, you release the trailer’s handbrake and walk round the lights.
From practice. A working method from lessons and practice. It is not a rule of the law or of CBR.