This website has an API that allows you to fetch current time, historical, and forecast data.
Link to WebsiteThis webpage gives you an introduction on how to use a custom search JSON API to add to your application. This Custom Search JSON API requires an API KEY which is provided in the page.
Link to Meteor's WebsiteThis API offers a free subscription that includes functions that retreive dog breed information, images, random dog images and much more. The API is used to create various dog related apps. All I had to do to receive the key was put in my email and my use for the key which was school project.
Link to Node.js WebsiteOverall, I am still trying to understand API's but this research documentation allowed me to get an idea of what many API's can be used for with the data provided. From what I was reading, API's are important to know when becoming a developer.