When you quote, summarize or paraphrase information you found in a source (book, article, etc.), you use in-text citations to give credit to the creator of the information. The purpose of the in-text citation is to give the reader the information needed to find the source in your references list. The in-text citation goes directly after the piece of information you included.
The references page lists the long citations for all the sources you cited in your paper and is included at the end of your paper. The purpose of a references page is to give the reader all the information needed to find the sources that you used. All citations are listed alphabetically, by the first piece of information (usually the author).