With pinggy.io you can share your Node-RED instance from localhost with just a single command. Replace the port 1880 with the port where Node-RED is running.
Pinggy will give you a URL like https://ranlkfsbjkxry.a.pinggy.link. Use this URL to open the editor, and as the base for any HTTP-in endpoint you want an external service to call.
Node-RED ships with no authentication on the editor, so anyone with the URL can edit your flows. Turn on Password Protect above, or set adminAuth in settings.js.
For the full walkthrough, see self-hosting Node-RED.