Where to start?
As mentioned, it’d be best if you’d already know some basics about HTML and CSS. If that isn’t the case you should probably go back and read a bit about it somewhere else!
Otherwise let’s continue with what you’ll need:
Browser
The easiest way to run JavaScript on your machine is inside the browser you’re currently reading this on.
If it’s not already Google’s Chrome one, I’d recommend you to download and install it. It offers some great developer tools which will come in handy later.
If you don’t want to use it, any other browser should be fine but you won’t always be able to follow the examples shown here on your end.
Editor
To write JavaScript code a simple editor is more than enough. There are some good IDE’s out there like WebStorm but I honestly don’t think you’ll need that at this point.
Until today I’ve worked with many editors like Sublime, Atom and currently Visual Studio Code. All three of them are absolutely free and offer a ton of extensions / plugins written by their great communities.
If you’d ask me which one to use now, it’d say Visual Studio Code.
It is very clean, beautifully designed and offers a ton of functionality around web development even without one of its thousand extensions.
If you settled on a browser and an editor, let’s continue!