When writing a research paper you will use a wide variety of resources. You are required to cite your sources for two main reasons:
For more information, check Why Do We Cite?
For help writing and citing APA Style, check out:
AGRICOLA, maintained by the U.S. Department of Agriculture's National Agricultural Library, is a database for all facets of agriculture and related fields, such as environmental studies, botany, and more. It offers comprehensive coverage of journal articles, monographs, proceedings, patents, audiovisual materials, and more.
GreenFILE offers information covering all aspects of human impact to the environment. Its collection of scholarly, government and general-interest titles includes content on global warming, green building, pollution, sustainable agriculture, renewable energy, recycling, and more.
Academic Search Complete is a database of academic journals, magazines, and other scholarly resources, covering a wide range of subjects across the humanities, sciences, and social sciences. It's a great starting point for research, especially with its inclusion of many open access publications.