Node.js and nvm and npm are already installed on your Cloud9 instance so you dont need to do anything to install them. If you want to install them on your laptop, you can follow these instructions.
My preferred way to install node is to use nvm. This lets you install multiple versions of node simultaneously, in case different apps need different versions. I don't usually need this, but I prefer nvm because it makes it easy for me to always get the latest stable versions of node and npm. It also installs into my local directory, rather than polluting the globally installed packages.
If you are on a Mac, be sure to first do this:
touch ~/.bash_profile
To install nvm, visit the nvm web page and copy installation command that uses curl so you can have the latest version. For example:
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.1/install.sh | bash
Then close your terminal, open a new one, and type:
nvm install stable
nvm use stable
You'll now be using the latest stable versions of node and npm. You
will need to repeat nvm use each time you open a terminal.
If you use Windows, you can install Node.js by directly downloading a package.
If you prefer, you can install using your package manager. I prefer to use nvm, because it is easier to manage multiple versions and get the latest version installed.
If you have Ubuntu, you can do this:
sudo apt-get install nodejs
sudo apt-get install npm
For Mac OS, you could use HomeBrew: Install Node.js and npm using Homebrew on OS X and macOS.