Simple uses of an API include:
Food delivery services integrating a mapping plugin which uses the Google Maps API to display courier locations on websites and apps.
Weather data being displayed in outdoor activity apps.
Traffic data gathered from an external source being displayed in your real-time transportation application.
An API is the mechanism by which the information exchange is facilitated and can facilitate more complex processes in either the source or destination system.
They can help create automated workflows between individual internal software systems, greatly reducing duplication of effort and improving organisational efficiency.