Windsheer,
There are two main types of approaches:
* Runway (or landing) approaches, and
* Circling approaches.
Runway approaches are those that position the aircraft on final approache, more or less in line with the runway & in a position from which a landing can be made with minimal manoeuvering. The idea is that the pilot becomes visual with the runway straight ahead & in a position from which a landing can be made. Precision approaches such as the ILS are an example of this, as are non-precision approaches such as a VOR/DME runway approach. The non-precision runway approach isn't able to have as low minima as a precision approach due to the greater buffer that must be allowed due to the lesser accuracy but the concept is the same.
Circling approaches, on the other hand, aren't necessarily trying to position the a/c on final and able to land straight ahead. Instead they're only trying to get the pilot visual with the runway at a height safe enough to manoeuvre around the runway & positon for landing. Think of it as becoming visual in the circuit area, rather than positioned on final. They can be arranged that becoming visual in the circuit area also is somewhat aligned with a runway, but don't have to.
Often a runway approach will also have a circling minima published on the same approach chart. This gives makes available two types of approaches using the same navaid. The pilot could do the runway approach with lower minima, or if another runway is more suitable, do the same approach to the higher circling minima then manoeuvre around the aerodrome to position for a landing on another runway.
Years ago the philosophy of 90 deg approaches to the runway for a circling approach was that the pilot would have a good opportunity to sight the runway crossing the nose, cross overhead & sight the windsock then be able to turn L or R onto a downwind for the favoured runway. This sort of thing would be done if a runway approach wasn't able to be provided
Nowdays it's considered the less the manoeuvering the better so most approaches are designed to be runway aligned, where possible.