Most styles have an official manual that can give you the most complete information. There are many great web sites that can help you with citing.
1.) Pick a citation style (i.e. APA, MLA). Ask your professor which style they prefer if you are unsure.
2.) When you quote, paraphrase or summarize someone else's work you need to tell the reader the source you are using. Two common methods to do with are in-text citations/parenthetical citations and footnotes/endnotes.
3.) Give the complete citation at the end of your paper in the bibliography or works cited page.
Whenever you quote, summarize, paraphrase or refer to the work of another person you need to cite it. Citing is the way to give credit to other's work when you use it in your papers, speeches and projects. Citing other's work is a very important step in the academic writing process and the best way to avoid plagiarism.
Tip: You do not have to cite anything that is considered common knowledge such as dates of events, well known facts, etc.
You need to cite other's words or ideas whenever you use them in your paper (i.e. direct quotes, summaries). This may include: