The API or application programing interface comes in handy in computer programming allowing software components interact with each other. A web API is the application programming interface specially created for web server and web browser. A framework for creating HTTP services that can be used by a wide range of clients including browsers, mobile handsets is the Asp.NET Web Api. Since it contains MVC features like controllers. Routing, filter, model binders it is very similar to ASP.NET MVC.
HTTP is a strong platform for building APIs that displays services and data, and not just an environment for serving up web pages. On any corner that you might look into there is a high probability to find a HTTP library, so HTTP services are able to reach a vast range of clients such as browsers, desktop apps and mobile devices.
In our days a web based app is not enough to reach for the customers, as people are very found to their gadgets and tend to use them frequently. Since using iPhones, tablets or any other device in our usual life we discover that we are moving from the web towards apps world. In order for the browsers to see your service data you should use an application programming interface for their compatibility with handsets devices and browsers. En eloquent example for the web apps and phone apps are the Facebook, Twitter and Google API.
Web API is an excellent framework for delivering data and service to different devices. The ideal platform for creating REST-ful services over .NET Framework is Web API because is open source.
Whenever you need a Web Service and not an SOAP, then the best choice would be ASP.Net Web API as it builds non-SOAP HTTP Services on top of WCF message pipeline and it does not have boring and extensive configuration like the WCF REST service. Web API is open source.