When you use other authors' ideas and words in your own writing, it is important to credit them - even if you do not quote their words exactly as written.
Citing your sources allows your reader to identify the works you have consulted and to understand the breadth and scope of your research. Footnotes, endnotes, and lists of works consulted provide substantiation for your own findings and ideas.
Practicing "cite as you write" and keeping track of ideas and quotations that you use in your own writing helps you to avoid plagiarism or charges of research misconduct.
Scientific citation styles vary by discipline. Many are based on the Chicago Manual of Style (B) . Some rely more on the APA (American Psychological Association) style. Detailed information can be found on the University Libraries web page: Citing Your Sources.
Most databases provided by the libraries have a "Cite" feature built in. Look for a link or button for citing. If the link is available, you will see a screen which provides a citation in your preferred format that you can cut and paste into your bibliography.
Many electronic resources offer citation creators and there are some that are freely available on the web. Feel free to use the links below at your convenience.
However, make sure you carefully edit the results before you paste them into your bibliography, citation creators are not always perfect. Automatic citation generation is only as good as the details made available from the database.
"Common knowledge" -- you don't need to cite where you found "common knowledge". But what is "common knowledge"? Guess what -- it varies. Here is a safe definition, because you don't want to be accused of plagiarism.
Did you know it without looking it up? If you are just learning about your field, you should err on the side of caution. Better to cite something that didn't need a citation, then to be accused of plagiarism.
Would other people in the class know this? Common knowledge is based, to some extent, on what the "general practitioner" in the field would know. And what would be general knowledge for a practicing electrical engineer MAY NOT be common knowledge for a freshman engineering student.
Do you find the information in many PUBLISHED (not web pages) resources? Some experts say if you find it in 3 reference tools, no need to cite. Others say 5. If you don't have time to check that the information has been used in many different places, cite it. Play it safe. The citation can be easily removed later and until the paper is in it's final version, you will know where to go back and verify the information.