Here's some terminology used in the tutorial that you might be unfamiliar with.
APIs are the filament that connects what i want to do with what i want to learn. Diana Kimball, Coding as a Liberal Art
Technically, API stands for Application Programming Interface. Practically speaking, it's really just a collection of (hopefully) well-documented functions and similar abstractions that allow you to do what you want to do with a programming language.
If a programming language is a language, then an API is a bit like a specialized dictionary, providing useful nouns and verbs that programs can use to do their job.
See the TinyTurtle API for an example.
A function is like a verb, or action, in a programming language. It's easy to create your own; see the Making new functions section of JavaScript for Cats to learn how.
In some programming languages, functions are referred to as procedures or subroutines. They're all basically the same thing.
JavaScript is an astonishing language, in the very worst sense. Douglas Crockford
JavaScript is a programming language created by Brendan Eich in 1995 under the time constraints of the First Browser War and some marketing constraints imposed by Netscape's partnership with Sun Microsystems. These contributed to it being a very misunderstood programming language.
Because of this, JavaScript is not a very easy language to learn, and it's a lot less readable than languages that lacked its constraints. However, it's also ubiquitous: it runs in web pages, which makes it extremely easy to share, and it can also be used to program robots, financial trading platforms, web servers, and a lot more. In other words, if there's something you want to do, there's probably an API for it in JavaScript, which makes it an extremely useful language despite its flaws.