Turnitin is a similarity detection tool, not a plagiarism checker. 
Your instructors may use Turnitin to check if your paper is similar to its content database, which contains online and academic sources, as well as student papers. The results appear with a percentage of similarity to other published works – this tool provides a starting point for your instructor to evaluate the citations and originality of your work. [1] Turnitin can also help your instructor identify areas where your writing may need support.
Only students in specific classes are able to check the similarity of their papers with Turnitin. If you are in one of those courses your instructor will provide access information.
1. West-Smith, P. (2022, October 5). Does Turnitin detect plagiarism. Turnitin.com. https://www.turnitin.com/blog/does-turnitin-detect-plagiarism
Turnitin has released a new ChatGPT detection feature. The AI writing indicator has been added to the similarity report as of April 4, 2023.
If your instructor has provided a Class ID and Class enrollment key, you can check your paper on Turnitin before submission to your Instructor. Verifying the similarity of your paper to existing sources before submission grants you an opportunity to add citations and paraphrasing.
Learn more about the registration process and submission steps in the following How-To Guides.