Before beginning an answer, it is important that you plan it properly so that it is structured to answering the question. The bullet points that go with the question will help you to do this. You must also refer to the examiner's assessment objectives to ensure you have met the criteria.
Below is a structure that you could use for your answer:
Point 3 from the above would form the main part of your answer and would be looking in detail at the extract.
Pip has a realisation at this point in the book. His realisation is that the money he has been given comes from a criminal background and that means he cannot belong to the upper class anymore and this means he will not be happy anymore. He will also not be able to marry Estella which would have probably upset his Victorian readers who liked happy endings. The word he uses to describe all this is 'stunned'. Dickens also writes a literary device about a shipwreck to explain Pip’s feelings which are not good at this point. All of this makes me feel very sorry for Pip because he has lost everything he cares about.
The older and wiser Pip (the narrator) looks back at a key moment in his younger life and development and uses a first person perspective to draw us and his original Victorian readers into Pip's moment of shock and realisation; his initial reaction is summed up in the verb 'stunned'. Pip gradually realises, however, that what Magwitch has revealed to him has changed his world completely. He begins to feel a sense of hopelessness and despair. The extended metaphor of a shipwreck is very effective in getting this across and helps us to sympathise with Pip's predicament that he will no longer be able to be part of the social class that he has longed to join. It also reminds us of the time when Pip was a boy and he watched the boats going out to sea while daydreaming about his future with Estella. He now realises that he has been fooling himself and that everything he has hoped and wished for is all a 'mere dream'.
Using the skills you have learned and revised, try answering the Great Expectations question. Time yourself and make sure you are meeting the examiner's assessment objectives.