My
grandfather built this house = This house was built
by my grandfather
Careless driving
causes many accidents = Many accidents are caused
by careless driving
We only mention the subject when it is important to say who or what is responsible for something. When this happens we use BY to introduce the agent in the passsive sentence. For ex: in the next sentence the agent would not be mentioned as it doesn´t add any relevant information .
Somebody cleans this class every day = This class is cleaned every day
With + instrument
It is used to talk about an instrument used by the agent to do something
the car was towed with a crane
With + material or ingredient
The
room was filled with
smoke
This cake is made
with brown sugar