Does a conclusion, introduction, body, or all of them contain a topic sentence in a essay?

When you write an essay you start with an introduction,and introduction means when you write about your topic and explain why you were writing about this certain topic.Next comes the body, The body means writing a few paragraphs about the topic and facts.After that comes the conclusion this is where you write about what happened after (e.g-how did this affect us?,What happened after war ended?) So yes this will contain a topic sentence in an essay.