as Dolf mentioned, the information you provided is a bit too vague to define which type of case interview you are going to have. In general terms, a case interview is defined as three major areas:
- Fit questions (eg Why do you want to work for our company?)
- Case (eg Your client wants to increase revenues using online channels, what would you suggest him to do?)
- Your questions at the end for the interviewer.
The general process usually takes 45 minutes: 5-10 minutes for the fit part, 30-35 minutes for the case, 5 for the final questions.
The best way to understand how the interview will be structured in your particular case would be to ask the HR manager information about the process and if there is any recommended material for the preparation. If they generally refer to a case interview, it is likely you will follow the previous mentioned steps.
Please let me know if you have additional questions.