Watch the following video, which elaborates on the definition of plagiarism. As noted in the video, you shouldn't let fear of unintended plagiarism keep you from drawing on the ideas of others. Instead, if you clearly understand what plagiarism is and you learn when and how to cite your sources—including works you have referred to even if you haven't quoted them directly—you can confidently build on the work of others during your academic career.
The video mentions the MLA (Modern Language Association) citation style. There are many more style guides, such as APA (American Psychological Association) style and Chicago style. Cline Library has compiled a list of commonly used citation and style guides for various academic disciplines.
In the video the instructor mentions TurnItIn, an online tool for preventing plagiarism. At NAU we use a similar tool called SafeAssign, which is available through the university's learning management system. If your instructor has set up SafeAssign in your class, you can post one of your papers to a drop box, and after a short while you will receive an originality report on the paper. For more information, review the SafeAssign Wiki. Pay special attention to the section on how to interpret reports.
A paper that scores more than 40% is likely to contain plagiarism. High scores are red flags to instructors, who will review your work carefully. Do yourself a favor and use the report feature to examine your writing before you turn in your assignments. Examine the items tagged in the report to see whether they might need additional citation.