If you are new to angular please refer to this article to know how to set up your first project in angular.

Webpack is a build automation tool used by angular to bundle the script files and style sheets and minifies them at runtime.
When we run the ng server command to run the angular application we can see a set of files compiled and minified. This bundling process is done using Webpack.

when we make any change in Html, style sheet or script files web pack will automatically rebuild the full application and reloads the web page.

Webpack also injects the compiled files reference to the index.html dynamically.
So a refresh is not required on the page to see new changes and this feature is called Hot Module reloading or Hot Module Replacement (HMR).