substring is a method of a string it returns only the value between the range
string input = "OneTwoThree";
string sub = input.Substring(0, 3);
Console.WriteLine("Substring: {0}", sub);
Result:
one
string input = "OneTwoThree";
string sub = input.Substring(4, 3);
Console.WriteLine("Substring: {0}", sub);
Result:
Two
substring('yourstring',startIndex,endIndex)
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