PHP - Php Apis

I really don't understand the point of an API. I am totally lost on this one. I have never in my life used JSON and barely touched Javascript so I'm already quite behind the curve but this was my understanding of the "purpose" of an API;   You have some data in a database that others might find useful so you write a script that allows people to go in and pull data from it.   So why aren't these APIs just built using PHP? If I have a database table of first names, last names and email-addresses, and for some reason I want other people on the internet to be able to get at that, then why don't I just write a one-page script that list them all out? Then all the user has to do is "include" it in their code, right?   That's probably really over-simplistic, and I am surely missing the point. There must be a point, but I cannot find a single source anywhere with an actual decent explanation of this. What am I missing?   You never know, perhaps you're all about to tell me that most APIs are built using PHP and what I've described is pretty much it. But everything I research leads to a dead end because they all refer to one another;   Example 1 - "Oh JSON is freaking awesome. I use it because it's awesome. It's awesome for work working with APIs".   Example 2 - "Oh, APIs, yeah, you totally have to have APIs. All you have to do is use JSON. It's awesome".   Not direct quotes, but close enough! Seriously, help me out. I have a lot of public data on my server and I am positive that someone can make good use of it. But how?