I’m going to do something else, something which I should have done a while back. That is explain a few more basic concepts which I may have taken for granted and while it maybe very simple. It does not hurt to go over things again.
Another way of looking at this is a google search. A user goes to the google page in a browser and does a search which brings back, hopefully, many results. Now there is an interaction with you the user and the data returned by google. For an API its very similar in that there is an interaction between the data source and your software. However the data is unlikely to be formatted like we see search term returns. It will be in a plain text format, this will make it lightweight and allow control over it, to format as required.
So to sum up. An application-programming interface (API) is a set of programming instructions and standards for accessing a Web-based software application or Web tool. A software company releases its API to the public so that other software developers can design products that are powered by its service.
For example, here is an example that I found, Amazon.com released its API so that Web site developers could more easily access Amazon’s product information. Using the Amazon API, a third party Web site can post direct links to Amazon products with updated prices and an option to “buy now.”