When you use someone else's thoughts, words, or information, you need to alert the reader, not only to give credit to the source, but also to give the reader a way to find the original. In-text citation points the reader to the appropriate source in your list of works cited.
You need to include the author's last name, or the title or shortened version of the title if there is not an author. In addition, you will need to include the page number or numbers unless you are referring to an entire work. If you have more than one work by the same author, you will also need to indicate which source you are referencing.
There are numerous variations of in-text citation that are acceptable, but they all give the information needed to locate the reference in the least obtrusive manner.
The following resources can be used to see more examples of in-text citation. They also provide more detailed instruction for a variety of different circumstances when additional information is needed to indicate the source.