Two way communication between arduino and a website using SIM 800 GPRS shield


I'm trying to read some data from vehicle based on inputs from a webpage.I have an arduino MEGA and SIM800 shield to connect to internet.I need to establish two way communication between a website and arduino.When a user clicks a button on the webpage,the name of the parameter to be requested is sent to arduino.Arduino request the parameter to vehicle and send its value back to webpage for display.

I have completed the vehicle communication part of the project but I need some ideas how to implement the web communication.Please help.