When I first got introduced to the world of the ESP8266, I had a real hard time to find a way to flash the firmware of the ESP8266-01 with an Arduino Uno. Many existing tutorials took essential information for granted or required additional hardware like a FTDI Serial TTL-232 USB cable, a USB-to-serial converter or a level shifter. Others were written specifically for breakout boards like the NodeMCU, SparkFun Thing or Adafruit Huzzah.
As I only had an Arduino and a barebone ESP8266-01 at my disposal, neither of these tutorials were viable. Eventually I managed to flash the ESP-01 firmware with pieces of information from Instructables, various blogs and youtube videos.
That’s why I wrote the missing step-by-step beginner tutorial on how to flash the ESP8266-01 firmware with an Arduino – it only requires an ESP8266, an Arduino, a USB cable and some wires to flash your ESP8266.