Ok, I read about the card, and Clarence is sort of right, but only if you have all three cards in hand. In that case, you will play both cards eventually. You would have to decide whether you want a chance of additional cycling, or if you want to hold on to the Copper the first time on the chance that you might hit a good price point before playing the second action. If you play Cellar first, then you can try to get a bunch of bigger treasures in hopes that you can hit a big handsize when you play Storyteller. On the other hand, if you have all your big money already, Storyteller first will probably let you Cellar your green cards.
If you want "Cellar-as-Storyteller", you have to throw in a Peddler and ignore everything but Copper.
