I just want to learn Arduino and make some small projects. But in the beginner starter kit there's a part named Prototyping Shield. Is it necessary or will it help me?
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.
You can make a slightly neater project with a prototyping shield. You can use much shorter jumper wires are sufficient to connect to the Arduino pins than if the proto was on your bench beside the Uno. That makes the project much more easily portable without knocking wires out of place. And if the project is one you want to make permanent, you've already laid it out for a shield and you're pretty near ready to start soldering parts and wires to the board.
The shield is certainly not needed for prototyping. I don't own any; I keep a handful of solderless breadboards around for the purpose. But if I were planning to build a permanent Arduino shield, that's where I'd start.