If this is the first time you have needed to file a tax return, you will need to register for Self Assessment and Class 2 National Insurance.
You can register online by clicking on the following link www.access.service.gov.uk/registration/email
You will then receive a letter from HMRC with a Unique Taxpayer Reference (UTR) number within 10 days. You will need your UTR number to file a return. You will receive another letter with an activation code for your account.
Once you’ve activated your account you can file your tax return any time before the deadline.