Challenges require you to complete a specific objective. Upon completion, you can receive in-game rewards like badges, Grand Stars, or rubies. Similar to Bingo, you'll get a reward of coins for completing three challenges in a horizontal, vertical, or diagonal line. Challenges are grouped together in collections with varying durations. There are Tour Challenges for each tour, Gold Challenges for those who subscribe to the Gold Pass, and Standard Challenges without a duration.
For more information on Gold Pass, please see the About the Gold Pass section of this FAQ.