The express.urlencoded() middleware function is used to extract the data from the request body and add it to the request object in the form of req.body. The extended option allows to choose between parsing the URL-encoded data with the querystring library (when false) or the qs library (when true).
When the extended option is set to true, the qs library is used to parse the URL-encoded data. This library allows for more complex data structures to be parsed from the request body, such as arrays and nested objects.
Overall, this code is configuring the Express.js app to parse incoming URL-encoded data from request bodies using the qs library, and adding it to the req.body object for easy access in subsequent middleware functions or routes.