Differences in string compare methods using C#

Different types of String Compare methods

public class Example

      {

            public static void Main()

            {

                  string testString1 = "String1";

                  string testString2 = "String2";

                  if (testString1.CompareTo(testString2) == 0) //or 1

                  {

                        //Condition

                  }

                  if (testString1.Equals(testString2))

                  {

                        //Condition

                  }

                  if (testString1 == testString2)

                  {

                        //Condition

                  }

                  Console.ReadLine();

            }

      }