nodejs separate code include middleware use()

I'm new to nodejs, below is my app.js I installed by express --sessions --css less --hogan app command.
I tried to separate the commented line in app.js move to a new file call route_handler.js.

I'm not sure am I doing correct I only add a require('./route_handler.js'); in app.js and should I have to export in route_handler.js but it is express() ?
How to solve it?

Does require means already execute the code in the file?

app.js

var express = require('express');
var path = require('path');
// var favicon = require('serve-favicon');
// var logger = require('morgan');
// var cookieParser = require('cookie-parser');
// var bodyParser = require('body-parser');

// var routes = require('./routes/index');
// var users = require('./routes/users');

var app = express();


// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'hjs');
// end: view engine setup


require('./route_handler.js');

// // uncomment after placing your favicon in /public
// //app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
// app.use(logger('dev'));
// app.use(bodyParser.json());
// app.use(bodyParser.urlencoded({ extended: false }));
// app.use(cookieParser());
// app.use(require('less-middleware')(path.join(__dirname, 'public')));
// app.use(express.static(path.join(__dirname, 'public')));


// app.use('/', routes);
// app.use('/users', users);

// // catch 404 and forward to error handler
// app.use(function(req, res, next) {
//   var err = new Error('Not Found');
//   err.status = 404;
//   next(err);
// });

// // error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});

module.exports = app;

route_handler.js

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

// var app = express();


var routes = require('./routes/index');
var users = require('./routes/users');



// uncomment after placing your favicon in /public
//express().use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
express().use(logger('dev'));
express().use(bodyParser.json());
express().use(bodyParser.urlencoded({ extended: false }));
express().use(cookieParser());
express().use(require('less-middleware')(path.join(__dirname, 'public')));
express().use(express.static(path.join(__dirname, 'public')));

express().use('/', routes);
express().use('/users', users);

// catch 404 and forward to error handler
express().use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// expore express() ??