You can access Turnitin via the Academic Skills organisation on Blackboard. Documents uploaded to Turnitin from this area are not added to the 'proper' Turnitin database, so you can use this area for multiple versions of draft work, without worrying that you will be accused of plagiarising yourself.
You can only upload one document at a time to this area. If you want to add a second document, you need to choose 'Resubmit' and write over the details of the first document.
Turnitin can take up to 24 hours to produce a report. If a document shows as 'Processing' for a long time, log out and check again later.