It signifies the person or thing that performs a particular action or has a particular function.
In the case of "conductor", it indicates the person or thing that conducts or directs something, such as:
* A conductor in an orchestra: The person who leads and directs the musicians.
* An electrical conductor: A material that allows electricity to flow through it easily.
* A heat conductor: A material that allows heat to flow through it easily.
So, the suffix "-or" in "conductor" tells us about the role or function of the thing or person being described.