Say, I wanted to get a certain value entered by a user in an HTML being run on NodeJS to be saved in my db, how would I do that?

I could get the value from HTML via the DOM, sure. Say example.html were being run via NodeJS like so:

var fs = require('fs');
http.createServer(function (req, res) {
  fs.readFile('example.html', function(err, data) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(data);
    return res.end();
  });
}).listen(8080);

I could get my value via the the DOM from example.html, like so:

var valuetobegotten = document.getElementById('valuetobegotten').value; 

But that only happens in the front-end HTML. I do understand that you need a MongoDB driver to be able to interact with MongoDB via NodeJS. And need to set something like this up:

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:8080";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  console.log("Database created!");
  db.close();
});

But, when I try to pull in valuetobegotten pulled in via the DOM earlier — by inserting it into a MongoDB collection, how does MongoDB know where to look to? Does it look to the url at JS files running on the same server? Like so:

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("mydb");
  var valuetogotten = valuetobegotten;
  dbo.collection("values").insertOne(valuetobegotten, function(err, res) {
    if (err) throw err;
    console.log("1 document inserted");
    db.close();
  });
}); 

Is that how it's done?