You need to acknowledge any resources you used by describing them in a way so that readers can identify and find the source. Citations usually include information on who is responsible for the text, what is the name of the text, who published it, where, and when. You must include a citation when you quote the exact words of a source, paraphrase the words, or use distinctive ideas found in the source.
You can learn more about citing your sources and creating bibliographies in the library's guide Understanding Citations, which will introduce you to both print and online resources for citation management. You can also watch this video from Purdue University for more information on citations.