A topic sentence essentially tells readers what the rest of the paragraph is about. All sentences after it have to give more information about that sentence, prove it by offering facts about it, or describe it in more detail. For example, if the topic sentence concerns the types of endangered species that live in the ocean, then every sentence after that needs to expound on that subject.
Topic sentences also need to relate back to the thesis of the essay. The thesis statement is like a road map that will tell the reader or listener where you are going with this information or how you are treating it