Esp8266wifi.h library not found error

Continuing the discussion from The smallest Wifi smartphone controlled 4WD car using ESP8266, Blynk and Arduino Code:
Hi sir, I have every possible way to compile the sketch and everytime an error occurs.
As I am only a hobbyist and no knowledge of coding and I have previously made a Wi-Fi car with help of tutorials mentioned in you tube videos and other sites.
I have been trying from last four days.
Can you please help me.
The error message I have mentioned earlier.