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