In C#, string is an object of System.String class that represent sequence of characters. We can perform many operations on strings such as concatenation, comparision, getting substring, search, trim, replacement etc.
In C#, string is keyword which is an alias for System.String class. That is why string and String are equivalent. We are free to use any naming convention.
string s1 = "hello";//creating string using string keyword String s2 = "welcome";//creating string using String class
using System;
public class StringExample
{
    public static void Main(string[] args)
    {
        string s1 = "hello";
        char[] ch = { 'c', 's', 'h', 'a', 'r', 'p' };
        string s2 = new string(ch);
       
        Console.WriteLine(s1);
        Console.WriteLine(s2);
    }
}| Method Name | Description | 
|---|---|
| Clone() | It is used to return a reference to this instance of String. | 
| Compare(String, String) | It is used to compares two specified String objects. It returns an integer that indicates their relative position in the sort order. | 
| CompareOrdinal(String, String) | It is used to compare two specified String objects by evaluating the numeric values of the corresponding Char objects in each string.. | 
| CompareTo(String) | It is used to compare this instance with a specified String object. It indicates whether this instance precedes, follows, or appears in the same position in the sort order as the specified string. | 
| Concat(String, String) | It is used to concatenate two specified instances of String. | 
| Contains(String) | It is used to return a value indicating whether a specified substring occurs within this string. | 
| Copy(String) | It is used to create a new instance of String with the same value as a specified String. | 
| CopyTo(Int32, Char[], Int32, Int32) | It is used to copy a specified number of characters from a specified position in this instance to a specified position in an array of Unicode characters. | 
| EndsWith(String) | It is used to check that the end of this string instance matches the specified string. | 
| Equals(String, String) | It is used to determine that two specified String objects have the same value. | 
| Format(String, Object) | It is used to replace one or more format items in a specified string with the string representation of a specified object. | 
| GetEnumerator() | It is used to retrieve an object that can iterate through the individual characters in this string. | 
| GetHashCode() | It returns the hash code for this string. | 
| GetType() | It is used to get the Type of the current instance. | 
| GetTypeCode() | It is used to return the TypeCode for class String. | 
| IndexOf(String) | It is used to report the zero-based index of the first occurrence of the specified string in this instance. | 
| Insert(Int32, String) | It is used to return a new string in which a specified string is inserted at a specified index position. | 
| Intern(String) | It is used to retrieve the system's reference to the specified String. | 
| IsInterned(String) | It is used to retrieve a reference to a specified String. | 
| IsNormalized() | It is used to indicate that this string is in Unicode normalization form C. | 
| IsNullOrEmpty(String) | It is used to indicate that the specified string is null or an Empty string. | 
| IsNullOrWhiteSpace(String) | It is used to indicate whether a specified string is null, empty, or consists only of white-space characters. | 
| Join(String, String[]) | It is used to concatenate all the elements of a string array, using the specified separator between each element. | 
| LastIndexOf(Char) | It is used to report the zero-based index position of the last occurrence of a specified character within String. | 
| LastIndexOfAny(Char[]) | It is used to report the zero-based index position of the last occurrence in this instance of one or more characters specified in a Unicode array. | 
| Normalize() | It is used to return a new string whose textual value is the same as this string, but whose binary representation is in Unicode normalization form C. | 
| PadLeft(Int32) | It is used to return a new string that right-aligns the characters in this instance by padding them with spaces on the left. | 
| PadRight(Int32) | It is used to return a new string that left-aligns the characters in this string by padding them with spaces on the right. | 
| Remove(Int32) | It is used to return a new string in which all the characters in the current instance, beginning at a specified position and continuing through the last position, have been deleted. | 
| Replace(String, String) | It is used to return a new string in which all occurrences of a specified string in the current instance are replaced with another specified string. | 
| Split(Char[]) | It is used to split a string into substrings that are based on the characters in an array. | 
| StartsWith(String) | It is used to check whether the beginning of this string instance matches the specified string. | 
| Substring(Int32) | It is used to retrieve a substring from this instance. The substring starts at a specified character position and continues to the end of the string. | 
| ToCharArray() | It is used to copy the characters in this instance to a Unicode character array. | 
| ToLower() | It is used to convert String into lowercase. | 
| ToLowerInvariant() | It is used to return convert String into lowercase using the casing rules of the invariant culture. | 
| ToString() | It is used to return instance of String. | 
| ToUpper() | It is used to convert String into uppercase. | 
| Trim() | It is used to remove all leading and trailing white-space characters from the current String object. | 
| TrimEnd(Char[]) | It Is used to remove all trailing occurrences of a set of characters specified in an array from the current String object. | 
| TrimStart(Char[]) | It is used to remove all leading occurrences of a set of characters specified in an array from the current String object. | 
