You are given 3 quests a day, which you need to complete within 24 hours. There's a timer at the bottom of the window that will help you keep track of whether you have enough time to complete a quest. Quests refresh when the timer runs out.
You can view the quests you've received by pressing on the chest located next to your guardian or on the middle button in the bottom right corner of the screen.
If you don't like the quest or it's too hard to complete, you can swap it for a new one by pressing the refresh icon in the top right corner of the quest! Free refresh is only available once every 24 hours, so be careful when choosing a quest you want to change.
Please note! A quest is only counted as complete if you explore a location or solve a puzzle successfully.