Each year, very many marks are lost by students for falling into this trap!
'Retelling' means telling about what happens in a story, play or poem. You gain no marks for this at all and so need to keep it to a bare minimum - just sufficient, when absolutely necessary, to make a point clear, for example.
If you know John Steinbeck's story, 'Of Mice and Men', here is an example of retelling:
'On page one Steinbeck is saying that it is warm and sunny in the Salinas valley and the mountains are golden...'
This will gain no marks as it is merely a description, albeit in different words, of the content of the story. What gains marks is a focus on, not the content, but on the methods used and the purposes intended. This means focusing your essay or exam answer on an analysis and interpretation of the content. This means working out the method used and the underlying meaning or purpose of the words on the page:
'Through his careful choices of powerful and emotional description, for example, "The water is warm too, for it has slipped twinkling over the yellow sands in the sunlight..." Steinbeck sets an initial scene of unspoiled nature, of a perfect, Paradise-like place; it is only when man arrives on this scene that things go wrong. This initial scene will later be contrasted in the reader's mind with that of the poverty of life in the "bunkhouse".