Getting started with Node.js and terminal?

Question

Command line

There is an article in Russian https://habrahabr.ru/post/243335/
It says:
Now open the terminal, go to the folder with your program and run the node helloworld.js command.
1) I understand that the terminal is such a black Windows PowerShell program ? (Everything in it is either white or red)
2) HOW to enter the folder with the program through the terminal?
3) Here I created a helloworld.js folder with the code console.log("Hello World!");
But how ??? execute command node helloworld.js ? What needs to be done? In this black Windows PowerShell program to write? But it gives me an error, says that the file is not found.
Before that, on a black background, I managed to get software versions
PS C:\Users\Anya> node -v
v9.3.0
PS C:\Users\Anya> npm -v
5.5.1

Answer 1

Is nodejs installed? Registered in the PATH environment variable?