void setup() {
  // initialize the digital pins as an output.
  pinMode(13, OUTPUT);
  // Turn the Serial Protocol ON
  Serial.begin(9600);
}

void loop() {
  byte byteRead;

  if (Serial.available()) {

    /* read the most recent byte */
    byteRead = Serial.read();
    //You have to subtract '0' from the read Byte to convert from text to a number.
    byteRead = byteRead - '0';
    Serial.print(F("byteRead = "));
    Serial.println(byteRead);

    int i,j;
    for ( i = 0; i < byteRead; i++) {
      for ( j = 0; j < 3; j++) {
        if (Serial.available()) {

            /* read the most recent byte */
            byteRead = Serial.read();
            //You have to subtract '0' from the read Byte to convert from text to a number.
            byteRead = byteRead - '0';
            Serial.print(i);
            Serial.print(':');
            Serial.print(j);
            Serial.print(F(":byteRead = "));
            Serial.println(byteRead);
        }
      }
    }
  }
}

for ( i = 0; i < byteRead; i++) {
    ...
    }