The government will take a portion of your salary when you earn above a specific threshold to repay your student loan. For Self Assessment, you will need to know which plan you’re on, so that your tax calculations are correct.
If you’re unsure what student loan plans are or are keen to learn more on the topic, the government website explains everything you need to know about the types of loans and what this means for repayment here.
If you’re unsure what loan plan you’re on, this might be on the documentation you received when you first applied for student finance. Alternatively, you can use the student loan balance site to check. In order to use this service, you’ll need a customer reference number or email address, a password, and your "secret answer".