We should cite in order
To be a responsible student by giving credit to other researchers and authors and acknowledging their ideas.
To avoid plagiarism (stealing) by quoting words and ideas used by other authors.
To allow your reader to track down the sources you used by citing them accurately in your paper by way of footnotes, a bibliography or reference list.
What is plagiarism?
Taking (stealing) someone else's work or ideas and passing them off as one's own.