See this guide for help with citing online sources in APA style.
What is plagiarism?
Plagiarism is using someone else's work without giving him or her credit, leading your readers to think those words are yours. While this might seem easy to avoid, many people who plagiarize do so unintentionally. Although most people think of plagiarism as recording someone's exact words without crediting him or her, it also includes re-arranging someone else's words (paraphrasing) or using his or her ideas. These forms of plagiarism are far more common and require careful attention to avoid.
According the Arizona State University LibGuide on Citation and Plagiarism, there are four main reasons to cite:
The main reason not to plagiarize is because doing so is unfairly attributing ideas of someone else to yourself, whether or not you intend to.
If you’re unsure whether or not to cite something, ask your professor or a librarian for help. Remember, it’s better to overcite than undercite!
Material from your paper that's from another source needs to be cited both in the text immediately after the cited material (in-text or parenthetical citation) and at the end of the paper in the works cited. However, if you mention information about the source in the text of your paper, you do not need to include that information in the citation immediately afterward.
For example ...
(Box adapted from LMU/LA Library APA Guide)