use express.static middleware to serve static css, html and js (client side) files
below indicates the public subdirection in main appication directory contains the static files
app.use(express.static('public'))
Now, you can load the files that are in the public
directory: (assumming listing at port 3000)
http://localhost:3000/images/kitten.jpg
http://localhost:3000/css/style.css
http://localhost:3000/js/app.js
http://localhost:3000/images/bg.png
http://localhost:3000/hello.html