In this short guide I will explain how to use the Arduino IDE version 1.8+ with ESP8266 based boards.

Start the Arduino software and open the file menu, preferences.
Click the button right of the Additional Board Manager URLs field.
Add the following address to a new line in the (empty) list:

Save and close the list

Go to the menu tools –> board –> board management
Select as type: contributed

Now you should have the possibility to install support for ESP8266 boards