What does citation mean?
Basically, citation stands for both
the cited information – either a direct quotations or a paraphrases of someone’s else words, and
the credit to source from which you have obtained it (even though it is better to refer to the later as a reference to avoid confusion).
Here are the phases with “citation” you are most likely to hear ))) with a short guide on how to understand them:
“Cite credible sources in your essay” – This means: Present ideas/facts/statistics from credible sources in your essay (in the form of direct quotations, close or summative paraphrases) and include the references to show where the information comes from
“This is not a general knowledge. You have to include a citation here!” – this basically means you have to add a reference to the source where the mentioned idea/fact/statistics has been voiced.
“Use three sources” = 3 sources (books, articles, etc.) vs “Include at least three citations” – citations may come from 1 source or 3 different sources, but you need at least three of them – you can easily count looking for the in-text references given in parenthesis or footnotes.
Reading this post about quoting paraphrasing and summarizing might give you a better idea about how to cite the sources