The topic is the general idea of the essay, the topic sentence specifies what is covered in the text, and the supporting details are sentences that have examples or facts that explain the topic sentence.
These key elements are a guide so that the reader can read the essay in a clear and coherent way without losing any detail of the essay.
A topic sentence states the main point of a paragraph. It is as a signpost for your readers, something that alerts them to the most important, interpretive points in your essay.
Topic sentences are simple statements of facts that cannot be disputed. But not all are completely factual, sometimes it presents an opinion about a topic and may not offer all sides of the story.