The 'int' return value of Socket.Receive represents the number of bytes received.

The byte[] parameter ('buffer') will contain the bytes themselves and, assuming they're being sent in the usual UTF-8 format, you can convert them to a string with:

string s = System.Text.Encoding.UTF8.GetString(buffer);

remember that socket.Receive can only read in only as much as you have space in your buffer. I typically use an 8k byte array because that's the default size of the tcp stack. you need to test the byte count Receive returns against the original size of your buffer, and if the received bytes is less than the buffer size, you'll want to stop receiving and decode the entire set of bytes:

int count = 0;
byte[] buffer = new byte[8192];
List<byte> data = new List<byte>();
while( true ) {
    count = socket.Receive( buffer );
    
    if ( count != buffer.Length ) { // done getting everything
        byte[] temp = new byte[count];
        Array.Copy( buffer, temp, count );
        data.AddRange( temp );
        break;
    } else {  // not done getting stuff yet, continue to read
        data.AddRange( buffer );
    }
}
string message = Encoding.UTF8.GetString( data.ToArray( ) );
Console.WriteLine( message );