Some basic theory questions for sending msgs through mobile

class SmsClass
   {
       SerialPort serialPort;
       public SmsClass(string comPort)
       {
           this.serialPort = new SerialPort();
           this.serialPort.PortName = comPort;
           this.serialPort.BaudRate = 9600; //what is BaudRate and why we use 9600 not other?
           this.serialPort.Parity = Parity.None;//if parity is for error checking then why we set Parity.None? 
           this.serialPort.DataBits = 8;// what is Databits?
           this.serialPort.StopBits = StopBits.One;
           this.serialPort.Handshake = Handshake.RequestToSend;// what is Handshake do?
           this.serialPort.DtrEnable = true;
           this.serialPort.RtsEnable = true;
           this.serialPort.NewLine = System.Environment.NewLine;
       }
       public bool sendSms(string cellNo, string sms)
       {
           string messages = null;
           messages = sms;
           if (this.serialPort.IsOpen == true)
           {
               try
               {
                   this.serialPort.WriteLine("AT" + (char)(13));// why we set char 13?
                   Thread.Sleep(4);
                   this.serialPort.WriteLine("AT+CMGF=1" + (char)(13));//also here char 13?
                   Thread.Sleep(5);
                   this.serialPort.WriteLine("AT+CMGS=\"" + cellNo + "\"");
                   Thread.Sleep(10);
                   this.serialPort.WriteLine(">" + messages + (char)(26));//why we set char 26 here? 
               }
               catch (Exception ex)
               {
                   MessageBox.Show(ex.Source);
               }
               return true;
           }
           else
               return false;
       }

this.serialPort.WriteLine("AT" + (char)(13));// why we set char 13?