Ethernet Shield Get a Variable from Remote Server


I am starting using the Ethernet Shield and I have some doubts, is it possible to get a variable from a remote server?

My project is to use Arduino to control a Vending Machine system, there will be many Arduinos connected to a remote server (each one will be a different Vending Machine) and it will work like a banking system. There will be registered users that will buy products and the Arduino must get in the server one variable that shows how much money does the user has, and if the user buy something, the system will update the remote server with the new value.

I am sorry if I was not clear but if there is something that I can explain better, please let me know.