Supplementary Job on Tier 2 General - how to file a tax?

I have started a freelance software related work for a company in Australia and need to get paid to my UK bank account.

As I am currently on Tier 2 Genera for the second yearl I am allowed to work up to 20 hours a week based on here: https://www.gov.uk/tier-2-general/second-job [nofollow]

However, I'm not sure how to file a tax as this is my first time. I have received 800 pounds for the work.

Any idea how I can do this?

Thank you