The thing to remember with citation is that it is simply a practice of creating a record of who said what, where, at what time.
Depending on what discipline you are writing in (English? History? Biology?), you may use a different style of citation. The main styles are listed below, with links that take you to different pages within this guide. If you are citing a source published by the government, you will cite it using special consideration.
Referring to a source, stating someone else's opinions, thoughts, ideas, or research
Using an image or media file that you did not create
Your thoughts and your interpretations
For more information and resources about plagiarism - intentional and unintentional: