00 Setting up enviroment
Considering you are using Arduino IDE. You can add the ESP8266 support by taking following steps:-
Start Arduino and open Preferences window.
Enter https://arduino.esp8266.com/stable/package_esp8266com_index.json into Additional Board Manager URLs field. You can add multiple URLs, separating them with commas.
Open Boards Manager from Tools > Board menu and find esp8266 platform.
Select the version you need from a drop-down box.
Click install button.
Don’t forget to select your ESP8266 board from Tools > Board menu after installation.