What is the necessity of "Prototyping Shield" for an arduino UNO R3?
A prototyping shield allows you to create your own circuit that can sit neatly on top of an Arduino.  Its main advantage is the pins/holes to connect to the Arduino, as these aren't evenly spaced so they are difficult to replicate with strip-board.
Do you need one? I doubt it very much, stick to the bread board and leave the soldering iron alone until you know what you are doing.