Your concept should have be made from two parts:

1. A short two or three world concept title, for example: "Over-the-top Hero*".
2. A one or two paragraph outline of the concept, for example: "He's a larger than life hero. He deliberately goes out and stands on a hill at sunrise just so he can pose with the sun coming up behind him. He always saves something - even if it doesn't want to be saved (the cat was actually quite happy up that tree until he showed up) and he never lets a photo opportunity go by".

Lastly, you should write the concept down - if only because the storyteller is going to ask you it.   * Ok that was four words - but you get the idea.