sendData, sendDebug - description of these commands

Using Arduino Programming Questions
#1

Good day.
I’m trying to write some program which will work with WiFi module esp 8266. I have found a lot of examples, but several commands in this code are not known to me.
Here is the part of listing:

#include <SoftwareSerial.h>
 
#define DEBUG true
 
SoftwareSerial esp8266(2,3);
void setup()
{
Serial.begin(9600);
esp8266.begin(9600); // your esp's baud rate might be different
sendData("AT+RST\r\n",2000,DEBUG); // reset module
sendData("AT+CWMODE=2\r\n",1000,DEBUG); // configure as access point

And another listing:

#include<stdlib.h>
#include <SoftwareSerial.h>
#include <OneWire.h>
#include <DallasTemperature.h>
#define ONE_WIRE_BUS 8
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);</p><p>
#define SSID "[YOUR_SSID]"
#define PASS "[YOUR_PASSWORD]"
#define IP "184.106.153.149" // thingspeak.com
String GET = "GET /update?key=[THINGSPEAK_KEY]&field1=";
SoftwareSerial monitor(10, 11); // RX, TX

void setup()
{
  monitor.begin(9600);
  Serial.begin(9600);
  sensors.begin();
  sendDebug("AT");
  delay(5000);
  if(Serial.find("OK")){
    monitor.println("RECEIVED: OK");
    connectWiFi();
  }
}

I understand, what these commands are performing, but why can’t I find them at the reference of arduino language??

#2

but why can't I find them at the reference of arduino language??

Because they are obviously functions in the sketch.

#3

... and you have not posted the entire sketch.

...R

#4