Hi Daina Alston ! Thanks for reaching out. I think what you're having trouble with is how to add a QuickMark to a paper-- it sounds like you might need to click the quickMark button in the sidebar before you highlight the text. Below is a screenshot of the step-by-step process, including highlighting text. You can also visit the QuickMarks guide directly: https://guides.turnitin.com/01_Manuals_and_Guides/Instructor_Guides/Turnitin_Classic_(Deprecated)/25_GradeMark/QuickMark
If you are still not able to add the QuickMarks you desire to your paper, I recommend reaching out to the Turnitin administrator at your school and/or our support team at email@example.com.
Hope this helps!