Skim over at the main title then the subtitles. I'm guessing that in the article, the subtitles change from happy, to sad, to maybe different topics or tones as the story or information continues. They are asking you to describe how those subtitles change.
I'd read the subtitles, the main title, and maybe a few paragraphs to get a feel of what is going on with the stories and what the pattern is, then write about the transmissions between those subtitles and any other information or patterns you think is worth mentioning.
Hope that helped! Send me the article if you're still confused.