Common knowledge does not need to be referenced, and you can assume that any reader is fairly knowledgeable about the field.
For example, a psychologist will be aware of pavlovian conditioning, so you do not need to reference that if it from your own head. There are a number of ways in which you can reference the source, but most are based upon variations of MLA and APA style.
You will need to create a bibliography or reference list of all of the sources that you use, but you will also need to indicate within the text where your information came from.
Referencing is an essential part of writing any research paper, so err on the side of caution.