why we use charat in java code example

Example: String charAt() method in java

// String charAt() method in java example
public class StringCharAtMethodJava
{
   public static void main(String[] args)
   {
      String strInput = "HelloWorldJava";
      char ch1 = strInput.charAt(1);
      char ch2 = strInput.charAt(6);
      char ch3 = strInput.charAt(10);
      System.out.println("Character at 1st index is: " + ch1);
      System.out.println("Character at 6th index is: " + ch2);
      System.out.println("Character at 10th index is: " + ch3);
   }
}