In the "All Flagged Words" section, you will see every word that you currently have flagged. If you press the "Select", you can process to tap specific characters that want to study. This feature is useful if you want to study old and new words in combination with each other. Once you have selected multiple characters, press on the bottom right button (i.e., blue question mark button). A circle will appear which will allow you choose from three quizzes: "Write", "Read", or "Pinyin".
Below are the possible pages that you will be brought to if you select one of the three quizzes: