You're assessed on (1) subject knowledge, and (2) communication abilities.
This means how well you know the material you want to be tutoring. We'll ask you about your grades on your application form, and ask you to upload a copy of your transcript as verification of your academic abilities.
Communication abilities means how clear you are at teaching, and how effectively you can break down complex concepts in an easy-to-understand manner. Communication abilities also refers to your friendliness, openness, patience, and in general, other soft skills that make you an effective teacher. We'll assess this during the video interview, where you will teach us something first-hand.