The phrase "not only...but also" is a conjunction used to connect two related ideas, emphasizing that both are important. It highlights the addition of a second point that enhances the first. For example, you might say, "The book is not only informative, but also engaging," which shows that the book has two valuable qualities. This structure can be used in various contexts, such as writing, speeches, or everyday conversation. It helps to create a more persuasive argument or a richer description. For instance, "The movie was not only entertaining, but also thought-provoking," illustrates that the movie offers both enjoyment and deeper insights.