Plagiarism:
Not sure what plagiarism is? Plagiarism.org defines plagiarism as using someone else's words or ideas and using them as though they were your own.
Plagiarism 101 with year 6 by LIRC Productions provides a great overview of the different types of plagiarism and how you can avoid it.
So to avoid plagiarism make sure you cite your source whenever you use:
another person's idea, opinion, or theory.
any facts, statistics, graphs, drawings-any pieces of information-that are not common knowledge.
quotations of another person's actual spoken or written words.
paraphrases of another person's spoken or written words.
(Source: http://www.readwritethink.org/classroom-resources/lesson-plans/research-building-blocks-cite-158.html?tab=4#tabs. Accessed 15 April 2015)
Citing your sources:
Not sure how to cite your sources? Check out Plagiarism.org's overview on citing sources or look at Heaton Intermediate LRC's information on how to cite your sources. Massey University's APA Interactive creates customised examples of APA references and also has a handy Introduction to Referencing.
Copyright:
So what's the difference between copyright and plagiarism? Although there is a lot of overlap, plagiarism is claiming another person’s words or ideas as your own while copyright infringement is using a creator’s work without their permission. This can include a song, a video, a movie clip, a piece of visual art, a photograph, and other creative works.
(Source: http://www.plagiarismchecker.com/plagiarism-vs-copyright.php; https://www.plagiarismtoday.com/2013/10/07/difference-copyright-infringement-plagiarism/. Accessed 17/04/2015)
Gives some general tips about what you are allowed to do with different types of other people's work as part of your school work under copyright law.