In the United States, giving credit to another author when you mention or directly quote something he or she has written, even if you are only quoting in a class paper that will not be published, is serious business and is governed by federal and state laws, and at USC by policies. Some countries and cultures approach this differently, and it can be an honor to copy an esteemed scholar's work. It is still an honor in the US, but you have to give the scholar credit! If you do not correctly indicate (that is what "cite" means) where you got an idea or a quote, you could be liable to discipline up to and including expulsion at USC.
It is pretty easy today to cite it right, since so many article citation and linking databases will help you construct a citation, so use those resources! (Here is an example from ProQuest, below).
There are different formats for citing other people's work. This can get confusing, we know! Make sure you know what format (for example, MLA, APA, Chicago Manual) your professor wants you to use, and be sure you use it!
For even more detail, we have a whole separate Research Guide on Citations.
Use the online version of Diana Hacker's to evalute your search results: