The GMAT is a computer adaptive test (CAT). This means that the test adapts to your performance as you progress through the exam. In this way, test takers all see a different version of the test.
The computer adaptive test is not just a computerized version of a paper-based multiple-choice exam. The computer actually adapts to your performance as you progress through the test. For success on the GMAT, you need to understand how computer adaptive testing works, as this can have a direct impact on your score.
Your Starting Score
When you begin a section on the CAT, the computer assumes you have an average score (~500) and gives you a question of medium difficulty. If you answer the question correctly you will be given a more difficult question which is worth more points; however, if you answer it incorrectly the next question you are given will be easier and worth fewer points, which will have a decreasing effect on your score.
You Cannot Return to Check Your Answers
Each answer you give (either correct or incorrect) affects the next question you will see - therefore the CAT does not allow you to go back to questions to check your answers. The CAT will only show you one question at a time and does not allow you to see the next question until you've answered the current one. Therefore, double-check your answer choice before moving on, as you cannot return to any question.
If you cannot answer a question, you will need to guess. Guess in a strategic way by eliminating any answer choices that you know to be wrong and then guess from those remaining. On the GMAT you will be penalised for every question that you do not answer - so if you only have a few minutes left and you still need to answer several questions, then you should guess at random rather than leaving them unanswered.