To start a game, you'll need to tap the "Daily Challenge" option in the main menu. By doing so, you'll be shown a screen with the remaining time to complete the challenge, your progress, and the number of crowns you can receive as a prize for completing it.
In this mode, you'll have to complete four streaks of 5, 10, 15 and 25 questions that need to be answered correctly and consecutively. When you complete each streak, you'll receive a prize and the progress will be saved, so that you'll be able to pick up the challenge in another time, starting from the beginning of the streak that you have reached. Keep in mind that since this is a daily challenge, the progress will be reset once the time is up.
If your answer is incorrect, you'll lose a life and you'll have to start again. If you have enough gold bars, you'll be able to pay in order to keep playing and not lose your turn.