How to understanding referents?

in which in this context is the same as where.

The initial step in forming a corporation is to file an application with the Secretary of State in the state where incorporation is desired.
in which or where refers the state the corporation is to be formed.

This elevator will serve the floor on which Company A is located.
In this sentence on which can be replaced with where too. We say on 6th floor, not in 6th floor and so on which is used instead of in which.

We put the proposition before the referent
The person from whom I receive the gift is an old friend of mine.
is preferred to
The person whom I receive the gift from is an old friend of mine.

Similarly
Recall the toys to which the new safety rule applies.
is better than
Recall the toys which the new safety rule applies to.

Which can be a subject or an object
Example
I know the driver of the car which crashed in the accident. (which is a subject of crashed)
The ring which she lost yesterday was found. (which was the object of lost)

Hope it helps.