The creature begins sharing his tale when Victor Frankenstein has grown more withdrawn and the tension in the story intensifies. This occurs approximately halfway through the book.
He must feel a great sense of loneliness. Throughout his life, he has been isolated and rejected. When telling his story, he may also feel a bit of hope, hoping that someone will finally understand his side of the story, his struggles and his longings.
The monster tells Frankenstein his story at a crucial point in the narrative, when Frankenstein is receptive to hearing his account.
Maybe she starts telling stories in the evening, when everyone gathers around the fireplace.
At first, the Creature is like a blank slate. He is born into the world with no knowledge but a strong sense of curiosity. As he experiences rejection from humans, he becomes bitter and angry. Eventually, he starts to seek revenge on Frankenstein.
The original Frankenstein story begins with a series of letters written by a sea captain named Robert Walton to his sister. Through these letters, we are introduced to Victor Frankenstein and his experiments.
He often starts with a setting or a situation that immediately grabs the reader's attention. For example, in 'A Game of Thrones', he starts with the discovery of the direwolves in the snow, which sets the tone for the mystery and danger to come.
Often, he'll start by mentioning a person or an event that triggers the whole story. For example, he might say 'I remember this one time when Flanders did such and such' and then go on to build the story from there.
Perhaps he tells his story in an abandoned castle. The solitude and history of the place might inspire him to open up.
It might be Walton, the explorer who meets Victor and hears his story. His perspective could be included in this part.
He feels a great deal of sadness. He was not given a fair chance at life.