Turnitin is a software program that can detect similarities between your written work and work that is existing in online resources. When you submit your paper to Turnitin, the software looks for similarities and issues a similarity report. It is not necessarily designed to prevent plagiarism specifically but it does help to minimize it.
At Saybrook, Turnitin is located in the Center for Writing and Academic Success course shell. The best place to learn more about Turnitin and access it is at the Center for Writing and Academic Success Turnitin page.