Once you create an assignment, you can specify a grading rubric for the assignment. You can use two types of rubrics: cumulative or itemized.
An itemized rubric breaks down the overall grade into several itemized grades, each with its own criterion. Students enter a grade for each item, and the overall grade is automatically computed.
Note: To ensure grading consistency, you can only edit the grading rubric before the review phase of the assignment has begun, and before any reviews have been submitted.
If you prefer, rather than creating an itemized rubric, you can just write the evaluation criteria, and ask the students to enter a single grade for the whole assignment. Students will write their review, and enter the grade.
Is it better to use a cumulative or an itemized rubric? This point is open for debate. The advantage of an itemized rubric is that students tend to be more consistent in grading: for each submission, the grades it receives will be more similar. However, we have observed that students using an itemized rubric tend to write shorter reviews, as they feel that they have already fulfilled their obligation to provide feedback by giving multiple separate grades.
You are free to experiment in your setting!