Help me understand some code

Question

using System;

using System.Text;

namespace forgetCode{

class Program

{

public static void Main(string[] args)

{

Console.WriteLine("Enter the string to reverse :");

string name = Console.ReadLine();

StringBuilder builder = new StringBuilder();

for (int i = name.Length - 1; i >= 0; i--)

{

builder.Append(name[i]);

}

string newName =builder.ToString();

Console.WriteLine(newName);

}

}}

Can someone please explain how this code reverses a string and why would you use stringbuilder over string?