This is really useful for so many use cases, for example temporarily sharing locally running services your building with colleges

1. Download Ngrok for your platform, from ngrok.com/download
2. Unzip the archive, and navigate to it's path or add an alias pointing to it
3. Simply run ./ngrok http [port num], so if your local app is running on port 300, that would be ./ngrok http 3000
4. The command line will show a public ngrok domain, which is accessible to anyone through the internet

You may need to log in, to do so, create an account on ngrok, go to dashboard --> autotoken and copy your token.
Then run ./ngrok authtoken [your-token]