A USI (Unique Student Identifier) is a reference number assigned to you by the Australian Government. It creates an online record of your training and qualifications attained in Australia.
You can apply for your USI here https://www.usi.gov.au/students/get-a-usi. Your USI can only be created once. You can retrieve your USI at https://www.usi.gov.au/students/find-your-usi if you have previously created one.
If you are not in Australia, please visit the USI website and generate a Help Request here: https://www.usi.gov.au/students/get-a-usi
You will need to verify your USI on Student Portal before collecting your timetable.