What is an annotation and how can I add one, or read those already added?

An annotation is extra information associated with a particular point in a film. When you 'scrub' the film (manually move the slider) you can find the annotations left by others and read them. You are also able to add them at any point by pausing the player during the movie, or “scrubbing” manually afterwards. Annotations do not show while the movie is playing because it would be distracting to those who simply want to enjoy the film.