<spoiler warning> A more detailed description here: Willy cannot face the reality of his mistakes and unsuccess, and k#lls h#ms#lf in a deliberate car accident. In the requium, his wife, children, and friends mourn his death.
Not directly, but one of the main characters crashes his car to k#ill h#ms#lf, and someone could interpret that as him crushing himself in the accident.
Ben comes to Willy as a hallucination; not being acknowledged by other characters and is only seen by him. It is not said directly that he is a ghost, though it could be interpreted as that.