Every day, Travian Kingdoms offers mini-quests that you can complete to earn rewards.
To view these daily quests, open the Quest book by clicking the corresponding icon with the exclamation mark on the left side of your village view. Then select the "Daily quests" tab.
There are three quest slots in your book. Each can contain a task. This means you can store a maximum of 3 daily quests at a time. Click on the quest name to view the task.
Once you've completed a quest, you can collect your reward, and the slot will be cleared. A new quest will appear after a short time with a countdown showing the exact moment.
If you're not interested in a specific quest or don't think you can complete it, you can exchange it for a new task by clicking the exchange icon at the bottom of the screen.