In what sort of context are you having to work with APIs?
It can be confusing to understand what an API is/does because it can serve a different purpose depending on the context.
When you make a post on this forum you're making a request to VIP2's server using an API which is expecting the request, and then handled by the browser.
An API can also be provided by a third party company like Smaddy's example which allows you to give external functionality to your users without having to leave your own website. For example, using Spotify's API to allow people to search for music.
In the examples above, API's are basically just URL's which allow you to perform some action on a server.