The Bazaar tab is where you can get useful rewards for watching ads. To open the Bazaar, you first need to tap the "Attack" button in your dungeon, and then the corresponding icon.

You’ll see different rewards you can receive there. All you have to do is choose the desired one and watch an ad.

If you don’t like any of the suggested rewards, you can tap the trash can icon next to them and wait for them to be updated.
The Bazaar is updated every 23 hours. However, you can speed up the process of updating a particular reward by spending 10 orbs.
Please note that only those rewards that you have removed by tapping the trash can icon or that you have already claimed will be updated. All other rewards won't change.
Among the rewards that you can get at the Bazaar are in-game resources (gold, emeralds, potions, etc.), as well as useful spells (for example, an additional chance to retrieve gems). Spells have a limited duration. You can view additional information about spells by tapping the i button next to the spell you're interested in.
To get the reward, you need to watch an ad to the end. If there are no rewards available at the Bazaar, then you should wait: they will appear later.