To help you practice during the whole duration of the course, you will use the following online editor tools. Pretty much all the course's examples will actually use these.
JS Bin is an open source collaborative Web development debugging tool. This tool is really simple, just open the link to the provided examples, look at the code, look at the result, etc. And you can modify the examples as you like, you can also modify / clone / save / share them.
Tutorials can be found on the Web (such as this one) or on YouTube. Keep in mind that it's always better to be logged in (it's free) if you do not want to lose your contributions/personal work.
CodePen is an HTML, CSS, and JavaScript code editor that previews/showcases your code bits in your browser. It helps with cross-device testing, real-time remote pair programming and teaching.
This is a great service to get you started quickly as it doesn't require you to download anything and you can access it, along with your saved projects from any Web browser. Here's an article which will be of-interest if you use CodePen: Things you can do with CodePen [Brent Miller, February 6, 2019].
There are many other handy tools such as JSFiddle, and Dabblet.