They work together, on both sides to provide a robust architecture for your application. You can write the server-side programming code using Razor syntax, and to handle all of the logic on client-side you can use AngularJS. No matter, whether you use AngularJS or not, Razor would be there in MVC.
To add the library to your web application, you should enter the script element in head section of your web application.
It would include the AngularJS for you. Even if you don't do so, you can still run the application, provide data to users, by writing the Razor code in your views. AngularJS would just make client-side programming a little simpler, why don't you read the documentation