Code minification is a technique to remove unnecessary characters from the source code. Minify your JavaScript (.js) and stylesheets (.css) files and improve the load time of your site by compressing the files.
In order to activate this process in Magento, navigate to the admin area (http://localhost/packt/admin_packt) and follow these instructions:

Content Delivery Networks, also known as CDN, are servers of fast access for your static or non-dynamic content. JavaScript files and images are examples of files hosted on CDN servers.
The main idea behind the use of CDN is saving the process time of your Magento server using a CDN solution.
I suggest you to conduct research on hosting services that provide this integration. For example, Nexcess as a Magento partner company provides specific documentation about CDN integration on the URL https://docs.nexcess.net/article/how-to-configure-cdn-access-for-magento.html.
For JavaScript CDN, we have a free-of-charge service available on the Internet! This is thanks to Google for providing us with this amazing feature at https://developers.google.com/speed/libraries/.