This question is in conjuction with How would you approach developing a Hotel Reservation System?

The solution to a system with different interfaces(or clients i should say) is to go with developing a Web service and have other systems interact with it.

I never had the requirement for developing a Web service so i am bit short on it. All i understand is that A web service is a system or application that performs some operations which may include modifying, sending or receiving data over a network using HTTP protocol. (Let me know if the understanding is wrong)

Now, from the other question it's clearly understood that i need to develop a web service but i have no idea as to how should i go about it. My language of choice is C# and .NET Framework.

Question:: How do we develop a webservice and which tools,technology and framework should i use for the same using C# language??

Question:: How can i interact with this from a desktop WPF application, Website and Mobile app