The first few days in a foreign country can be a blurry process of getting to your university, checking into a hotel or your residence halls and trying to settle down as best as you can even with all the jet lag.
As an international student in the UK, however, there are several responsibilities that you have to carry out within the first few days of arriving. One of these is the requirement to register with the police within seven days of arriving.
Take note that this is a legal requirement made by the Home Office, as provided in the Immigration Regulation Act 1972 (Registration with the Police). Failure to register with the Police is a criminal offence and could lead to prosecution.