I want to know how courses and subjects run in universities.

Hi
I am not very familiar with these course modules or subjects in UK universities.
So plz can you help me understand this?

So, basically, I don't have any idea how courses and subject system works.

I understand that if you choose a specific major(generally one), you'll get some core subjects and optional subjects.
But can I choose to attend in other subjects that are neither of them both?

for example, if I major in Accounting, but want to study philosophy subject as well.


I'm really looking forward for your answers
thanx