You can import many external library in angular via npm install --save <nameOfLibrary>. This library will be place in the "node_modules" directory and will be known throw your package.json. This is for all the EXTERNAL libraries. When you'll upload your code on git, you won't upload the node_modules, because those externals libraries are public, there is no need to upload.
Now when you are creating a component in your angular project, you got two ways to call it.
First, like you said, with the HTML tag <app-contact-form></app-contact-form>
(the name og the tag come from :
@Component({
selector: 'app-contact-form',
templateUrl: './contact-form.component.html',
styleUrls: ['./contact-form.component.css']
})
- with a routing in the module: many website explain it. One exemple : https://www.codingame.com/playgrounds/8104/angular-router-tutorial