Each topic is split up into quizzes, and each quiz is made up of several learning objectives. Each learning objective has a number of questions, the system will randomly choose which question to ask you.
Each wrong answer in the system is linked to a misconception. You must correct misconceptions before moving onto the next learning objective. This way, you know why you got a question wrong and are given an opportunity to improve before moving on.
The system tracks your knowledge retention over time and shows you when it is time to refresh and review each quiz.