Almost all JavaScript courses out there tend to mix two things together which must righfully be kept separate: the core language and APIs provided by the browser in the language. This separation ensures that you know what parts of JavaScript are the same across different environments (such as Node.js) and what parts change.
The former part has already been covered in the JavaScript and Advanced JavaScript mini courses. This mini course is dedicated to the former part, i.e. browser APIs. Browser APIs are simply utilites provided by the browser in JavaScript to achieve some useful thing in the browser.