Well, Angular is Angular. Angular CLI is a command developed in Node that helps you generate the boilerplate of an Angular project, so you don't have to do the repetitive, error prone work of preparing a new project by hand. This command uses npm to download the different dependencies the generated boilerplate needs.
Angular CLI let's you start a development web server too, to assist you during the development.
This is a very high level explanation. If you are totally new to Angular + .NET Core development, I would recommend you to check this book. It helped me a lot when I was in your position.