Publish NodeJS Server Online

Question

I'm having trouble port forwarding my modem to my Node.js server right now. I apologise if this is a repeat question; I've spent some time researching familiar themes.

I'm using the express framework, and I've attached a little clip to show you what port the node is listening on.

The js server is also listening.

(Quick Question: Do I use server.listen or app.listen in this situation? What's the difference?)

var express = require('express');
var app = express();
var server = require('http').Server(app);

app.listen(4000);

I've also attached a photo that includes:

The node.js server is up and running, as well as ipconfig (to show my local IP address) and a screenshot of the port forwarding settings on my modems.

When I google "What is my IP Address" and get my public IP address, I get an error message on my browser that says the server took too long to answer. I'm guessing the server isn't being port forwarded, but I can't seem to pin down the problem.

I'd be grateful for any assistance.