Node.js is an open-source, cross-platform runtime environment for developing server-side Web applications.
Simply download and install the package for your operating system. To check if you have node installed, for Windows open the Windows Command Prompt, and for Mac open up Terminal and type:
node -v
This should print the version number so something like this would show up:
v4.4.0
Congrats! You now have Node.js installed. Now you can browse the NPM website for packages and install awesome ones such as the GitHub Markdown Preview.