Given that you are new to the preparation, I would like you to understand that Case Cracking exercise is introduced in consulting recruitement because in many ways it simulates the consultant's work. This is a role play in which you as a candidate is playing a role of a consultant and interviewer is playing the role of a client.
When you hear the situation and the issue from the client. You do the fllowing things in this perticular order.
1. First you ask the client clarifying questions so that you have a good grip on client's situation and you know what the client wants
2. Ask for a few moments from the client, absorb the answers that client has given to the clarification questions and build your approach to solve the problem. THIS APPORACH IS NOTHING BUT STRUCTURE. It is called structure, because as the name suggests the appraoch needs to be STRUCTURED - preferably in ISSUE TREE fromat and following MECE principles. I suggest that, you write your structure on the paper and not just remember it mentally because, throughout the interview you need to navigate through it. You don't want to forget part of it in the heat of the moment.
3.Communucate the approach/structure to the client. Get his agreement and move onto the first analysis (in candidate led cases) or wait for the next question (in interviewer led cases).
Hope this helps! All the best!