Plagiarism consists either of failing (often unintentionally) to properly cite the work of others that you use in your own work (thus making it appear as if you created the work for which others should actually get credit), OR of intentionally presenting someone else's work as your own.
An example of unintentional plagiarism might be paraphrasing (putting in your own words) the ideas of another without properly citing the original author/creator's work. An example of intentional plagiarism might be purchasing a paper online and turning it in as your own work; Unintentional or not, plagiarism amounts to stealing other people's work.
It's important to note that even if you put someone else's idea into your own words, if the idea did not originate with you, failure to cite the original creator is considered plagiarism.
Luckily, there are ways to avoid engaging in plagiarism! Scroll down to the "Avoiding Plagiarism" section below to learn more.
The primary way to avoid plagiarism is to cite your sources (and to do so properly!)! The following resource from Plagiarism.org defines plagiarism, gives specific examples of what constitutes plagiarism, and explains how to avoid engaging in it. Click on the link and read the article there.
Now go to Step 5 to learn how citations in APA style are created.