Freshers will allow you to join clubs, societies, etc.
Your course will also run introductions to staff welcome meetings.
Any reasonable sized campus takes a while to learn to navigate.
Many courses do not take place in one building. Example is Warwick which is 700 odd acres.
On average you have ten mins between lecture slots.
While some leeway is given for late arrivals you need to find your way to everything from SU to admin, lecture halls and departments.
You make friends in freshers, you may become best mates or even sleep with some, learn to hate others and join a random society that is a passing interest or becomes a lifelong passion.
There are booze filled events, religious societies, “cool/uncool” activities but it is a finding your feet week that you will miss out on if you don’t attend.