What kind of an introduction you do will depend on how long your paper is supposed to be. If you are just writing a summary, you will probably just start with a first sentence that tells the author, title and main idea. Then the rest of the first paragraph should give the basic overview of the main points of the article. Several examples of this are given above. If you are doing a longer summary, or a response and a summary, you might want to start with an introduction that gives your own experiences or background on the topic before you began to read the article.