Blizzard included a tutorial about the cutscene editor in the Collectors Edition of Heart of the Swarm.

Long story short, here it is:

I watched it on the DVD and enjoyed it for the most part. My only real issue with it is that it teaches you how to make cutscenes using existing story mode models made for their cutscenes rather than doing it from scratch.

It is so much better than the mapmaking tutorial they have on there as well. That poor guy was so stiff.