After you have taken your exam and received your scores, what happens next? What does your score mean? How will it be used?
Each institution that you designated to receive your score can interpret and use your GRE scores as it sees fit. Some schools are concerned only about the verbal score, other schools are concerned only about the math score, while other admission committees are concerned about the writing score. Yet other schools are interested in a combination of the three. All of this is dependent on the school and program that you are applying to. Also, keep in mind that your GRE score is, generally, just one single component of the graduate school application. Other aspects of a graduate school application, such as past academic performance, the quality of recommendation letters, your personal essay, etc., can have as much or even more of an influence on you getting accepted than does your GRE score.
Regardless of how the schools to which you are applying interpret or decide to utilize your scores, ETS provides several guides on how scores should be used and interpreted. There, you'll also find the scoring guides for the analytical writing section; these are the guidelines that are used by the essay readers to give you a score, so it might be a good idea to look at those guides to see what exactly the essay readers expect.