从前 (cóngqián) is the key that unlocks the world of Chinese stories, from ancient legends and fables told to children to an elderly person's nostalgic reminiscences.
While it has a classic feel, 从前 is still actively used in modern speech and writing.
The most common point of confusion for learners is distinguishing 从前 (cóngqián) from 以前 (yǐqián).