Some English structure problem

Management is conferred to the directors who were chosen primarily by the shareholders of the company.

Management is conferred to the directors, who were chosen primarily by the shareholders of the company.

I would like to know which part of the first sentence is modified by the word "who".

And how about the the second sentence? What is the function of the "," prior to the word "who"?

A street-sleeper has made his home with old cartons and blankets on the street corner near the mail box.

I also would like to know which part of the sentence is described by the word of "on" and "near".