MKR1000 rx and tx

Hello, everybody!
So I have to do a project for school and I chose to make an CO2 detector that sends email notifications if the CO2 levels are to high to trusted contacts.
So I need to help on how to send the data to Blynk, the sensor uses RX and TX.
Also, I don’t actually know what RX and TX are/do, so can someone explain?

arduino: MKR1000
Android blynk version 2.27.1
Blynk server

code from arduino:

unsigned char hexdata[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}; //Read the gas density command /Don't change the order
void setup() {
  
  Serial1.begin(9600);
  while (!Serial1) {

  }
  Serial1.begin(9600);

}

void loop() {
   Serial1.write(hexdata,9);
   delay(500);

 for(int i=0,j=0;i<9;i++)
 {
  if (Serial1.available()>0)
  {
     long hi,lo,CO2;
     int ch=Serial1.read();

    if(i==2){     hi=ch;   }   //High concentration
    if(i==3){     lo=ch;   }   //Low concentration
    if(i==8) {
               CO2=hi*256+lo;  //CO2 concentration
      Serial.print("CO2 concentration: ");
      Serial.print(CO2);
      Serial.println("ppm");      
               }

  }   
  
 } 

 }

Do you have a data sheet for your CO2 detector?

Pete.

On this site you can find all the details you need.
https://www.dfrobot.com/product-1565.html