How does it work?

It's pretty simple. It works like this:
You view this website from your network. That tells our server your IP address.
Our server then uses the tool of choice for network scans, nmap, to scan your IP for open ports.
If it can find open ports it will try to determine the service on that port and the version. The latter is important because certain versions of products may have specific vulnerabilities - a hacker would know this.
Once the scan is complete, which should take around 5 minutes, a webpage will appear with the results.