Plagiarism has to do with taking credit (deliberately or accidentally) for someone else's work or information. To avoid committing plagiarism, it is important to attribute the source of your information.
Copyright infringement may be committed even if credit is given to the original creator. It pertains to unauthorized reproduction of someone else's intellectual property.
As students and educators, we do have some leeway in the reproduction of portions of copyrighted works for nonprofit educational use that fall under the fair use guidelines. In general, this means only a small portion of the work may be used and the reproduction must not adversely affect sales of the work.