Since the previous post did a good job at explaining the MLA style and has even provided a website, let me say a few words on what you need to put into the annotated bibliography. In an annotated bibliography, you basically want to summarize the article in the most succinct way, so that the reader will be able to get the main point or the basic gist of the article or work. In order to do this, you need to spell out the thesis of the article along with the main supporting points. You may also want to give one sentence on the value of the work for the project in view. With a little practice, you will get the hang of it.