Hi,
After you are finished answering all the question in bith the sections, you will have your score displayed on the screen. On this screen, click 'Review screen' link on the bottom right hand corner. Once on the review screen, you can select to review either all questions or the flagged ones only. Unfortunately, the GMATPrep provides only the correct choice and not the method applied to reach the answer. If you have any doubt on the solution, you can always post the qusetion on the relevant forum and have it discussed.