Why APIs are Important?
In the simplest terms, APIs are sets of requirements that govern how one application can talk to another. APIs aren’t at all new; whenever you use a desktop or laptop, APIs are what make it possible to move information between programs—for instance, by cutting and pasting a snippet of a LibreOffice document into an Excel spreadsheet. System-level APIs makes it possible for applications like LibreOffice to run on top of an OS like Windows in the first place.
Biggest Example is UBER used by all of us.
Uber has been integrated with various other third party tools for its services like-
a) Location Services
b) Notifications
c) Payment Processing
d) Promotional Advertising