How to fit a metallic back box on a stud wall?

Hey everyone,

I'm trying to understand how to fit a metallic back box on a stud wall. Should it be fixed to a stud (on one of the sides) or is it expected to be fixed to a noggin?

In either case, how would I know exactly where a noggin or a stud is, so that the hole I cut on the plasterboard is perfectly aligned with it?

I have a stud detector, but there is always a degree of error, so I'm not sure how I can find these in the wall.

Thanks!