Every quiz question you get wrong in the lessons is added to your review queue automatically. Miss one and it comes back tomorrow. Get it right and the gap grows to two days, then four, then nine, then three weeks.
Reviewing something just as you are about to forget it is far more effective than re-reading it the same day. This is the same idea behind flashcard apps used for languages and medicine, applied to investing basics like compounding, diversification, fees and order types.