How To Generate Random Charecters Using C#, I Tried The Code Below But It Doesnt Work

Use LINQ,
It will generate the 5 digit random characters.
var chars ="BCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
var random = new Random();
var result = new string(
Enumerable.Repeat(chars, 5)
.Select(s => s[random.Next(s.Length)])
.ToArray());

// use static classes and methods where possible
// Don't use System.Random it is not secure
private static readonly RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

private static void Encode(char[] data, char[] lexicon)
{
    //Don't let null values break your code
    if (data == null)
    {
        throw new ArgumentException("data");
    }
    if (lexicon == null)
    {
        throw new ArgumentException("lexicon");
    }
    var randomNumber = new byte[1];
    int size = data.Length;
    //use char[] rather than a string.
    //Strings are not very secure as copies are made in memory each time a string  is changed
    for (int i = 0; i < size; i++)
    {
        //Load random number into buffer.
        //Use methods that return 'void' where possible.
        rngCsp.GetBytes(randomNumber);
        int index = randomNumber[0];
        data[i] = lexicon[index % lexicon.Length];

    }

}

private static void Main(string[] args)
{
    string lexicon = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    int size = 8;
   var data = new char[size];
    Encode(data,lexicon.ToCharArray());
    string password = new string(data);
}