what is the purpose of web services? Ans. To make the application on a web server.
I mean isn't all web applications a web service ? Ans. Yes
also why do people create API web services? is it to let Aeveloper's use the website's functions? kinda like facebook and youtube ? Ans. To give other websites of web applications ability to interact with their website or database.
Is it possible to make a API for web service where you can use C++ or VB to use the functions? therefore, someone could make a desktop application based on your web application's API ? Ans. Yes
How do you create a web service API and a web service ? Ans. You can use technology like SOAP with XML to do this.
Hope my answer provide you the information you are looking for.