Each of the Sign Offs are broken down into individual ranks.  You must ONLY work on and complete the lessons that you're qualified to work on. 
For example, a YM LCpl cannot work on, take the quizzes or take the final exam for any ranks above a YM Cpl.
Each of the lessons are broken down into the performing objectives for you to master. 
Remember, this is not about just getting a sign off.  Knowing and understanding the material so that you can teach it to junior Young Marines under you is important. 
Take the time to understand each chapter - this is not a race.  You may take the quizzes as many times as you wish. 
When you are ready to take the test for your sign offs, go to the FINAL test page.  The test is timed and you cannot leave the page once the test starts.