Storyboards are similar to scenarios: They illustrate the interaction required to achieve a goal. But instead of using a list of steps, a storyboard visualises the interaction similar to a comic strip. Here is a sample board I created to explore another interaction for our new website:
The storyboard above describes how the persona Mary books several employees on the same training course. The board consists of a series of frames. Each frame shows sample data. Underneath it, I added a brief description of what Mary does at each step.
Note that I have done my best to describe the functional aspects of the interaction, and not to design the user interface: When I was working on the board, we did not have any design sketches and mock-ups available. I generally find it good practice to capture the product functionality necessary to meet the main user needs before designing the user interface.
Using user-stories + scenarious + storyboarding:
Creating scenarios or storyboards for selected epics allows me to explore the user interaction in more detail, to describe the necessary steps and their relationship. This helps me test my assumptions, for instance, by creating a paper prototype that implements the scenario in order to carry out an early user test.