You need to include a citation whenever your work contains or refers to someone else's:
In-line citations or foot/endnotes (depending on the assigned citation style) should be inserted at the point-of-use in your assignment and indicate that the information you just presented came from a source other than your own brain or common knowledge.
A bibliography and/or works cited section should be included at the end of your assignment.
There are hundreds of bibliographic styles, each with its own precise formatting. The most popular at CapU are MLA and APA.