You can read a helpful explanation of what constitutes plagiarism provided by the Plagirism.org web site, or take a 25-minute tutorial "How to Recognize Plagiarism" from Indiana University Bloomington.
Here's a short (10-item) quiz. If you are taking the short quiz, keep track of how many incorrect responses you have as you go along. The web site also offers a longer certification test, but you must register to take it.
Purdue's Online Writing Lab (OWL) has a web page that explains Quoting, Paraphrasing, and Summarizing.
You must cite sources from which you quote or paraphrase in your research paper. For rules and examples of the APA citation style, look here:
Sometimes students will use online citation formatters provided free on the Web or within a library database. If you use one of these online formatters, remember that they are not foolproof. You will need to review your citations to make sure they are correct. UW-Whitewater's libraries have a guide that lists some of these citation formatters.
The American Political Science Association has a style manual: