https://medium.com/jungletronics/meet-iot-boards-esp8266-esp32-ba12e41c1a3b

heltec_oled_hello_world.ino

/*  
      Project : FreeRTOS - How to Get Started!
   
   Episode 01 : Hello world ESP-32 - Using Heltec WiFi LoRa 32
       
         File : heltec_oled_hello_world.ino
         
      Webpage : https://medium.com/jungletronics/meet-iot-boards-esp8266-esp32-ba12e41c1a3b
       
     Hardware : https://heltec.org/project/wifi-lora-32/
 
 */

#include <heltec.h>
#include "Arduino.h"

  // the setup routine runs once when starts up
  void setup() 
{

  // Initialize the Heltec ESP32 object
  Heltec.begin(true /*DisplayEnable Enable*/, false /*LoRa Disable*/, true /*Serial Enable*/, false /*PABOOST Enable*/, 470E6 /**/);

  Heltec.display->flipScreenVertically();
  Heltec.display->setFont(ArialMT_Plain_10);

}

void loop() 
{

  // clear the display
  Heltec.display->clear();

  Heltec.display->setFont(ArialMT_Plain_10);
  Heltec.display->setTextAlignment(TEXT_ALIGN_LEFT);
  Heltec.display->drawStringMaxWidth(0, 0, 128, String(millis()));
   
  Heltec.display->display();
  delay(10);

}