Yes, you are absolutely right. When i teach others GitHub, i would like to explain the concept via an example. Lets take a scenario in which the teacher is conducting an MCQ in his class. He usually make copy of the question paper and distribute it (Forking) to his students so that they can work on it and mark the correct answer. The teacher still has the master copy. On the completion of the test he can collect the copies from students so that he can assess it(Pull request).
Simply just like it. Forking is a concept of making copy of the main repository to your account so that you can make modifications in it. You can Submit pull request to the main repository with the modifications. It will make sure that the main repository is prevented from unwanted changes.