Arduino Mega and Wifi Shield Communication

Im using a Arduino Mega and Wifi Shield for a project in which i need to control the arduinos movement (its sort of an RC Car) and recieve sensor data from it over the web, ive looked into using it as a webserver with interactive buttons etc. to allow control. The issue is i dont know where to start, ive worked out how to use the arduino as a webserver to display simple sensor data (using the example sketch for a webserver) but i dont know how to make it so you can send data back to the arduino.

Anyone know what to do?

thanks in advance :)