It is much easier to remember something that you had an active part in learning, rather than something that was simply lectured to you. This is why Pokemon players can memorize the type-matchups chart after just a couple hours of battling but people have much more difficulty memorizing the contents of a slideshow. Participating mitigates this somewhat.
Their would imply that it mentions a human. However, in this case, it's describing a nonliving thing, or "tomorrow." Their should only be used in the case of humans, or a grouping of humans.