Copyright infringement occurs when a copyrighted work is reproduced, distributed, performed, publicly displayed, or made into a derivative work without the permission of the copyright owner.
As a general matter, just don't use something that doesn't belong to you. Simple enough? If you do, we will find you, hunt you down, and hand you over to the good guys (while making a ton of memes of you in the process). So please don't plagiarize. Its not fair to the authors, and causes you sleepless nights.
Please also note that the information provided should not be considered legal advice.