How do universities decide if they want you?

Hi!
(I'm kinda new to TSR so sorry if I've done anything wrong haha)

I'm just wondering, when universities come to decide if they're accepting you (once you've done your exams and you've got your grades) do they simply look at the 3 (or more or less) grades you got eg ABB
Or do they look at the individual exam grades you got. Because, say someone got A's in 2 of their modules, but then got a D for another, their overall grade will not be an accurate representation of their achievements in each module?
I'm saying this because I got an A and a B in my english lit coursework, and feel reasonably confident about one of my exams.... but the last exam went awfully I don't want to get a C or a D overall and the grades for my coursework and other exam grades be overlooked?
Thankyou to anyone who can help me out, it would be really helpful!!!!