Questions about testing code setup

I’m very new to programming but decided to try to learn Javascript while stuck at home. After going through the first few lessons I got to the point where Codecademy teaches you how to set up your computer to code. I’m using the terminal on my mac with VS Code and I feel like I have a basic understanding of how those two work together. I’m very confused with how testing my code works and how to set it up on my computer, though.
This article was provided along with a few others, but none have any in depth information on how to actually test my code. I was hoping someone might be able to point me to more resources to learn how to be able to test my code. Thanks for any help.