It is very easy, to know where to find the story keys in Genshin Impact, you will have to reach an adventure rank 26 to then unlock the Story Quest function and thus be able to earn Story Keys by completing 8 daily missions which are equivalent to two days of commissions, once you complete your eighth mission you can ask for your key to the story.
To claim it you must go to the "Events summary" page, enter the chapter that is currently running, you will see a message to claim your key, you can claim it and add it to the inventory.
We remind you that you can only have a total of 3 Story Keys at a time.
The Story Keys can be used in special missions, which have a fairly high level of AR so they require you to meet certain requirements before playing them, if you meet them you can use your keys in the various chapters of a story.
These are the necessary tips that you should know to be able to find the keys of the story in Genshin Impact.