For people employed in the UK repayments are automatically deducted at source via the PAYE system.
If you are self-employed or living abroad your repayments will need to be set up with the Student Loans Company directly, and will not be taken out at source.
If you move abroad, your repayment amount is based on the equivalent level of living costs of the country in which you reside. More information, per country, can be found via this link which shows current rates and is constantly updated.
For information relating to how interest is charged on student loans and how repayments are made see the videos and links below:
Understanding Repayments: https://www.practitioners.slc.co.uk/exchange-blog/2017/december/understanding-repayment/