How It Works API?

API allows an application to communicate with other applications on the Internet through a series of calls (call). An API, by definition is something that defines how two entities to communicate. The entity here is a real different software (in service) denagn other software. With API calls - call back - through inter-regulated through a web application service.
Web service is a collection of technical standards and protocols, including XML (Entensible Markup Language) is the common language used by the application - the application for communicating on the Internet.
API itself is a set of software code is written as a series of XML messages.