Shakespeare only had a small, bare stage on which to present his plays. Obviously he could not show Lear wandering on a heath, as might be done in a motion picture. He had to use words in order to create the illusion of a barren heath, and then when the audience sees Lear they understand that he is supposed to be on the heath, having stopped to rest dirty and disheveled after wandering for a long time without shelter, food, or water. Something similar would be done in a motion picture. The King and the Fool would come to a halt at a marked position where a camera had been set up too enact what is contained in Act III, Scene 2. But before that there would probably be long shots of the two characters wandering in the open, since the motion picture camera offers much more freedom than a stage with a wooden floor. You will see in many of Shakespeare's plays that action is described rather than shown. A good example is the battle at Philippi at the end of Julius Caesar. Another good example is the murder of King Duncan in Macbeth, which takes place offstage.