There really is no set structure for section B, because you can literally choose to write in whatever structure you like! Most people might be more comfortable with writing in the standard English structure - intro, body paragraphs, conclusion, but you don't have to.
Personally, I find writing the intro/conclusion to be a waste of time as on the final exam, you won't actually be marked on it. The structure I used for section B was multiple paragraphs of in-depth analysis without an introduction or a conclusion, with each paragraph dissecting a particular idea with a specific example or two. This ensured I would get my message across effectively and efficiently without large chunks of text that confuses the reader, while allowing me to go into a lot of detail and showing my knowledge of the text by bringing in examples.
Of course there are many different ways of structuring a close passage analysis. I recommend grabbing some sample ones from past examiner's reports or high scoring students and seeing which one you'd be most comfortable with.