ręku

In a sentence

• Trzymałem kwiaty w ręku.

  I was holding flowers in my hand.

  In this sentence, 'ręku' refers to the physical hand in which the subject is holding something.

• Na ręku miałem zegarek.

  I had a watch on my wrist.

  Here 'ręku' refers to the wrist area of the hand, where a watch is typically worn.

• Podniosłem coś z ziemi prawą ręku.

  I picked something up from the ground with my right hand.

  In this sentence, 'ręku' is used to specify which hand (right) is involved in the action.