Answer: When you do contest you will earn your rating. Rating is calculated similar to Elo rating. If you can solve hard questions, you will get higher rating. Each user will have a separate rating for different contests i.e AMC 8, AMC 10, AMC 12, AIME. We don't rate any contests before 2000. The difficulty of each question is not arbitrary, it's based on MAA data.

Answer: You can improve your rating by solving harder contests. One way to prepare for contests is by learning the Courses

Answer: You can find everything about your performance in My math space. You can see your solve rate by subject i.e algebra, geometry, number theory, counting and probability. You can see your performance by contests.

Answer: You can find everything about your past questions by checking My math space. You can review your past questions and earn your reward by doing quest video tutorial.