It is not possible for you to register independently to use the web version on - so if you are being asked for a 'Class ID' you are in the wrong place.
Please note: the only access the University provides to Turnitin is via Canvas. Not all courses have provided Turnitin access to students, so if you are in any doubt please check with your tutor. If you can’t see the Canvas course, you should check within your individual modules to see if there is a practice upload link within the Assignments area.