Install Node serve for running your javascript code from this url
https://nodejs.org/en/download/
Open your terminal and type the cd command followed by the name of the folder your want to access e.g
cd BigO-Notation or cd javascript-syntax
If you wish to list all the files in the folder use the following command in your terminal
ls
You can run your javascript file by starting with the node followed by the name of your file e.g
node conditions.js
If you wish to return to the root folder use the following command
cd ..