C# String Tutorial
A string in CSharp is an object of type String whose value is text. The string type represents a string of Unicode Characters . String objects are immutable that is they cannot be changed after they have been created. String is an alias for System.String in the .NET Framework. Initialize a string with the Empty constant value to create a new String object whose string is of zero length.
From the following links you can see some of commonly using C# string operations in detail.