Marks Explained :
The mark given is out of 20, and is intended to reflect accuracy of content. The closer you were to answering the question, and the level of accuracy in your answer, the closer to 20 you get.
However, the comments I have given concern writing style. They will become of importance later in the course as the essay writing becomes more 'creative' or philosophical. Do have a read and come to me with any queries. A good writing style can be natural but it can also be acquired by practice and guidance. Besides which, we can all find room to improve so don't be disheartened by criticism, in philosophy it doesn't equate to being 'wrong'.
For future essays and your final exam/coursework you may want to take a moment to check out the 'Essay Advice' link on this site. It may give you some ideas on construction and emphasis in philosophical essays.