Difference between ng add <package name> vs npm install <package name> in angular 6

ng add

ng add <package> uses your package manager and installs the dependency. That dependency can have an installation script which can be used to do more job except the dependency installation. It can update your configurations, download another dependencies based on that one or create scaffold templates (with initial markup and logic).

To use ng add for a third party dependency, that team must provide schematics which describes the installation script. This can include some .scss or .css or related .js files to be included in the angular.json file.

In your provided link, you can install material package and also create some components with components

npm install

npm install <package> just installs the dependency.

For more Version 6 of Angular Now Available.

ng add

Will use your package manager to download new dependencies and invoke an installation script which can update your project with configuration changes (In angular.json file as well), add additional dependencies (e.g. polyfills if needed), or scaffold package-specific initialization code.

For example you run the command ng add @angular/material — Install, it will automatically install the package and configure in angular.json file too.

npm install

Whereas npm install <package> will only install your package into your project but will not configure in order to use.

For example you run the command npm install jquery it will install jQuery in your project but you need to configure manually in .angular-cli.json file (as in v5)

For more information read out here -

• https://blog.angular.io/version-6-of-angular-now-available-cc56b0efa7a4