After the installation process finishes, run the following command while still in your workspace directory:
The ng serve command launches the server, watches your files, and rebuilds the app as you make changes to those files.
The --open (or just -o) option automatically opens your browser to http://localhost:4200/.
Alias for ng serve --open.
ng serve --open or npm start commands,
you may have an older Node.js version, try updating your Node.js to the latest LTS version and then try again.