When you present ideas that are not your own, you must include a citation.* There are three ways you may present someone else's ideas:

• "Direct quotations,"
• paraphrases,
• and summaries.

A direct quotation is when you use the exact language of another source. Quotations must be placed in quotation marks to show that these words originated somewhere else. 

A paraphrase is when you take an idea and place it in your own words. Like a quotation, you can identify the exact location you found the idea in another source. Therefore, when paraphrasing, include page numbers.

A summary is when you describe an idea that is overarching in another source. When summarizing, you are using your own words, but describing someone else's idea and you may not have an exact page to reference.

*But what about when I want to say something that I did not discover on my own but it seems like common knowledge? There is common knowledge in all fields that does not require a citation. For example, a citation would not be needed to claim that the book of Acts is a continuation of the Gospel of Luke. No informed reader would assume you were claiming that was your original idea. While common sense can generally guide you towards what to cite versus what not to cite, there are grey areas. Your best course of action when unsure is to consult your instructor. Failing that, it is better to err on the side of overcitation than undercitation.