Your administrator can set defaults that will apply to all assignments you create. One option they have is to automatically have Turnitin active.
Index all submissions - This option will add files automatically to your organization's private repository. This makes them available to be matched against in similarity reports by other people within your organization.
Allow students to view Similarity Reports - This setting determines if students are able to see similarity reports that are generated.
Bibliography and Quotes - Allows you to automatically exclude bibliographies and quotes from the similarity reports. Want to know more? Check out the guide.