A key element to avoiding plagiarism is making sure you cite your sources properly. In economics, you will likely use the American Psychological Association's (APA) citation style, but make sure you check with your course instructor for the style they require. Purdue OWL's APA Citation Resourceswebsite which gives examples of how to cite various source formats (ebooks, print books, ejournals, videos, etc.).
Purdue OWL's website also has resources on other citation styles.