Nowadays everyone has an API and it's fairly common to want a website you're working on to fetch data from a 3rd party API. That's because pulling 3rd party data into your website can not only enriches your website's content, but doing so can prevent the need to duplicate commonly needed data.
API provided data could include displaying weather information, going through drupal.org projects, looking through census results, or even displaying Magic the Gathering card data. In fact, every WordPress site comes with an active JSON API out of the box.
There really is an API for almost anything. It's no surprise that you'll eventually want to consume some random API while developing a Drupal website. But enough of the sales pitch, let's get started consuming JSON APIs. Read more about Consuming JSON APIs in Drupal 8