When you have an idea, one of the most practical but easiest ways to define and describe it for others is video prototyping. In video prototyping you usually simply use paper drawings and record a short video to visualize your idea.
The video prototype shows which user role (persona) wants to reach which goal with which benefit. Or also which problem is solved with which service or product. A step in between a user story and a video prototype can be a storyboard.
At the “rapid paper based video prototyping” the usage of a paper prototype with changing states is filmed in a way that the interaction and reaction manner of the system becomes clear. Basis for that is a screen flow.
A list of tasks that should be accomplished in video prototyping has been mentioned on the MediaLabAmsterdam website.
Here is an example of video prototype for a mobile app.