You need to install and set up Node.js on your machine. Go to the official Node.js website (https://nodejs.org/en/download/) and download the latest version, depending upon your operating system.

I am covering the installation for the Ubuntu here. Let's go through the steps:

1. Open your Terminal and run this command:

curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -  

This will add the Ubuntu repository entry for Node.js version 8+.

2. Now, run this command to install Node.js:

sudo apt-get install -y nodejs  

After a while Node.js, along with NPM, will be set up.

3. To check the version of Node.js and NPM, run the following command:

node -v
npm -v 

The output is as follows:

You can run a similar command in Mac as well as in Windows (using PowerShell or Windows Command Prompt).

This should ensure that Node.js is set up properly and we can proceed with the Cosmos DB MongoDB creation.