We grade AWA essays just like they're graded on the GRE - by an e-rater which is a computer program, and then verified by a human grader with experience in this field.
If you're a free user, your essay will be graded only by the e-rater, and not the human grader.
If you're a paid subscriber and need any feedback regarding your essays, you can reach out to us via chat, and we'll be glad to help.