How do I create a search engine (an extension of work from the Express, Pug authentication course)

When the user runs a search, they are sending a search to the server. The server would take that search (whatever text they've entered) and use it to search the database, and then display a list of results that meet the criteria.

So first, you'd write a custom javascript object/function/class that knows how to take a string of text, and search your database. It's custom because how it does this, extracting keywords etc depends on the structure of your data.

Once you have that, in express you'd have something like

app.get('/search/:query', function(req, res) {
  let results = searchEngine.runSearch(req.query);
  res.render('results', { results: results });
});

Then you just need a pug template for the search page (with the text input) and the results page.