The ESP8266WiFi.h header will now be available for use in your sketches. Key Features of ESP8266WiFi.h
Search for and click Install on the package by the "esp8266 Community". Select Your Board : esp8266wifi.h library download arduino
Locate the "Additional Boards Manager URLs" field and paste the following URL: https://arduino.esp8266.com/stable/package_esp8266com_index.json . : Go to Tools > Board > Boards Manager . The ESP8266WiFi