Difference between a server with http.createServer and a server using express in node js
Ultimately, express uses node's http api behind the scenes.
express framework
The express framework provides an abstraction layer above the vanilla http module to make handling web traffic and APIs a little easier. There's also tons of middleware available for express (and express-like) frameworks to complete common tasks such as: CORS, XSRF, POST parsing, cookies etc.
http api
The http api is very simple and is used to to setup and manage incoming/outgoing ,HTTP connections. Node does most of the heavy lifting here but it does provide things you'll commonly see throughout most node web framework such as: request/response objects etc.
Express uses the http module under the hood, app.listen() returns an instance of http. You would use https.createServer if you needed to serve your app using HTTPS, as app.listen only uses the http module.
Here's the source for app.listen so you can see the similarities.:
app.listen = function(){ var server = http.createServer(this); return server.listen.apply(server, arguments);};