Give credit where credit is due; cite your sources.
Citing or documenting the sources used in your research serves two purposes, it gives proper credit to the authors of the materials used, and it allows those who are reading your work to duplicate your research and locate the sources that you have listed as references.
Knowingly representing the work of others as your own is plagarism (see the Library's plagarism resources page).
Consult with your instructor on how to cite resources and which style to use. An overview of citation and writing styles is available.