Exploring the digital world!
APIs are purpose built application program interfaces. Good APIs usually serve as the universal portal to a system, anything you can do through the purpose built application can also be performed programmatically through the API. This allows systems to integrate.
Practice working with different APIs:
The Twitter API was difficult for me to obtain. I had to provide details on how I planned to use their service before being allowed to examine the service.
Google also requires you to have a billable account before providing may of their API keys.
Music and audio platform: https://developers.soundcloud.com/
Accept credit card payments: https://stripe.com/docs/api
Display feeds that matter to you: https://www.instagram.com/developer/
Make notifications: https://www.twilio.com/docs/api
Improve your local business awareness: https://www.yelp.com/developers
Up you travel game: https://skyscanner.github.io/slate/#api-documentation
It will take effort to learn how to use each API.