If you write an essay about your favourite television show, you probably want to <em>inform</em> your audience what you consider is so good about it and <em>why you think it is important for others to watch it.</em>
Explanation:
If you think the best format to express why you think that show is the best show on tv, you probably think that you need to give precise information and data in order to be clear for your audience, otherwise, you would just write a short article or you would tweet about it. But, you think the essay is the best way because you think of it as a deep subject, you have reasons, you have information and you want everyone to know how this show is so great and why they should watch it too.
A central idea is focusing on informational texts, while themes are a life lesson that an author wants you to take away after finishing their story. =)
