I'm using Grails to create cool sites. It has own template engine, controllers, routing rules and etc. AngularJS also has template engine, controllers, routing rules. When should I use Grails / when should I use Angular JS? I'm new to AngularJS so it's hard for me to implement whole things using only AngularJS + JSON server response
The standard approach seems to be to build a REST interface on the server side and use that to communicate with Angular. I don't know Grails, but I am sure there will be some plugins / libraries for creating a REST API, or you could write your own.
The most common type will take your requests and return JSON objects back to angular.
Step 11 of the angular tutorial shows how to connect Angular to REST. http://docs.angularjs.org/tutorial/step_11
As Allessandro pointed out, this is a very broad question, and you will likely have to do a lot more reading to get something working, but this is the most common approach.