In writing, the introduction of the main idea is crucial for guiding the reader's understanding of the text. Authors typically use a topic sentence or thesis statement to clearly present their main idea at the start of an article or paragraph. This statement serves as a roadmap for the reader, indicating what to expect in the following content. Additionally, throughout the article, authors often provide supporting details and evidence that reinforce this main idea, helping to clarify and elaborate on their argument or perspective. Understanding how an author introduces their main idea can enhance a reader's comprehension and critical analysis of the text.