The TEA has a document (found here) that explains how essays are graded. You can access the rubric using the link previously mentioned, or you can access it in the Google Drive linked to the right.
Remember, when your essay is graded it is given a score of 1-4. Two people grade it, and then add their scores together. In order to keep the writing and reading portion equal, the TEA made the decision to multiply the summed scores by 2. The total possible points for the essay is 16. Some teachers provide students their scores in a form of 1-4 (they divide your total points by 4), some teachers provide students their scores in a form of 1-8 (they divide your total points by 2), or they provide you the total out of 16. All are correct and acceptable as long as you know what form your score is in.
I like to think of the scores in a simplified way. If you score a 1 out of 4, it means your writing is confusing. You either didn't pick ONE side, you didn't provide reasons or evidence, or you hardly wrote anything. If you score a 2 out of 4, it means your writing is basic. It's not too confusing, but you definitely need to work on providing reasons and evidence. If you score a 3 out of 4, it means your writing is good! You made sense, you probably used examples and evidence, and you definitely had a strong thesis statement. My goal is that all students get a 3 out of 4. If you score a 4 out of 4, you amazed the grader. You did just about everything right!