The Tavern displays quests that can be completed for semi-random rewards. The tavern unlocks at Level 28, and any Heroes used to complete Tavern Quests can still be used as usual in other areas of the game.
Quests can be anywhere between 1★ - 7★'s in tier. Upon choosing a quest, you can manually choose the Heroes you want to assign to it, or the game can auto-assign heroes that meet the quest requirements. Quest requirements can be any combination of heroes from a certain faction, of a certain ★tier or of a certain class.
Higher tier quests have better rewards, but take longer to complete and have harder requirements to meet.
Once started you can wait for the quest to be completed or immediately finish 1★ and 2★ quests or pay Gems to complete higher tier quests early. It is not recommended to pay Gems as quests complete themselves automatically in the background, and the rewards are the same.
Quests reset daily, and quests that have not been started may be refreshed at a cost of 10 Gems per quest. Refreshing low tier quests gives another opportunity to get higher tier quests which have better rewards. The amount of quests available can be increased temporarily through Basic Quest Scrolls and Senior Quest Scrolls. It can be increased permanently through different tiers of VIP.
Locking a quest will 'save' it from being auto refreshed the next day. By locking a quest you also lock 1 of your refreshes i.e. if your maximum is 5 quests but 1 is locked, you will get 4 new quests the next daily refresh and will still have the locked quest.
Another way to 'save' quests is to complete the quest, but not redeem it. This locks your heroes to the quest, but will grant you a new quest the next day i.e. if your maximum is 5 quests, but 1 is completed and not redeemed, on the next daily refresh you will get 5 new quests and keep the remaining un-redeemed one.