Actual use of Jade template and angularjs

Jade creates the html used in the browser on the server-side. The browser executes a request to the web-server, the web-server executes Jade, which will generate the html that will be sent to the browser. This server-side content generation has been very common in the last ~20 years, but it has quite some cons when building rich internet application. Mostly this has to do with performance and client state tracking.

AngularJS is a client-side MVC/MVVM like framework to build so called Single Page Applications (SPA), which allows you to have the complete user interface flow, all content generation and state tracking to be done at the client side. It even allows you to build offline applications. From the developer point of view this feels much more like building a desktop application where the client knows the state of the user interface. From the user point of the view the website will respond much smoother and snappier because the UI is all generated locally.

Note: SPA does not mean that you can only have one page in your website. It's a technical term where the browser downloads one page (~/index.html), which contains the complete or partial web application. The user technically never leaves this page, but the content (pages) is dynamically swapped in and out from this placeholder page.

To most common way to provide data to a SPA is via RESTful web services. AngularJS comes with builtin support for REST.

Some developers combine server-side content generation techniques with AngularJS, but there's actually no real need for this.

Jade is used as a template engine on both server-side and client-side. Yes, it can update a page dynamically, you just have to compile your jade templates to a javascript functions (using jade -c or something similar).

Yes, you can use angular.js with it, but I see no real need to use two template engines in your project. Suggesting to just stick with jade, unless you know what are you doing.