Citing Sources is more than just creating a Bibliography! Whenever you use another person's language, ideas, or other original content, you need to acknowledge this both within the body of your paper using in-text citations and at the end of your paper in the bibliography or reference page. You must give the proper credit to the original source to avoid plagiarism.
Citing sources is also the best way to show the research you have done on your topic.
The way you document your sources depends on the writing style manual your professor wants you to use for the class (e.g., APA, MLA, Chicago, etc.), and is usually specific to your discipline or area of study.
MLA Example from LMU's Citation Style guide