There are a number of citation styles available to use, and it's important that you use the correct style for your class.
The most common style for psychology classes is APA (American Psychological Association), and the library has many resources available (online and on campus) to help with citing. Below are a few useful links:
There are a number of reasons why you should provide a list of references at the end of each paper or project, as well as cite these references in the actual text.
Citing your sources is good form, but it also helps the reader to distinguish between your own thoughts and those of others. It is also important in avoiding plagiarism, which is the intentional OR unintentional use of another's work without citing.