Ember CLI Addons won't show up in browser

I got big hopes when I heard of package-managing for Ember.js. After several tries I'm quite disappointed. Maybe I got something wrong. Lately I'm not even getting one specific addon to work.

So in docs there are always command lines like:

npm install --save-dev ember-cli-components

So I did that. But nothing worked. Still wanna-have component em-modal is not available in my Ember App.

I fiddled around with bower install. Nothing worked.

What am I doing wrong? In every doc of every plugin installing seems super easy, but not for me?