The Academic Integrity Handbook, is a great guide for learning about citations, citation styles, and academic writing.
It is expected that you use other experts' and scholars' ideas and even quotations in your writing; however, you must explain where you got this information by using citations. A citation is the information about a source that you used. The goal of citation is to point the reader back to the original source of the information. Citations also inform your professor that you have used suitable sources of information in your work.
When to cite?
Whenever you are presenting words, ideas, images, or data from someone other than yourself, include a citation for that work. You must also include a citation when paraphrasing or summarizing, as the idea is still coming from another source.