Once the demo has been installed and you land at Lave Station you will receive the message asking you to undertake a "mission". The
Obsidian Ant YouTube video is the best one I've seen of the start of the demo. You answer the questions and play along as OA demonstrates. The demo then takes you on a journey asking you to undertake various things and you also get some narrative about one of the characters with whom you interact.
As I mentioned above this is a simple, linear story but shows the possibilities that this technology can offer. If the interest is real enough we may well see further chapters in the stories with a more complex, non-linear storyline for us to play with. The demo is well thought out except, perhaps, the journey to Hutton Orbital but this was done deliberately to give them time to relate other parts of the story that would otherwise requires a lot more development to achieve. Remember, this is a demo to judge the interest in the product.
Does that help?