Give credit where credit is due. By properly citing the sources you use in your research projects you are both identifying the resources that you used to complete your work and you are formally acknowledging the authors or creators of those resources.
It's always best to ask your professor what style you should use in your projects. You can find the digital style guides below, and print style guides at the Research Help desk in the library lobby.
You'll find many references in the course of your research. Make sure you keep track of what you find! Citation Management Systems are excellent tools to organize your references.