Understand the nested promise

MultipleNestingPromise.js

var app = angular.module('app',[]);
app.run(function ($http, $q) {
 
  getExample($q)
    .then(function(value){
       console.log(value);
    });
  
})
function getExample($q) {
    return resolvePromise($q).then(function(resultA) {
        return resolvePromise($q).then(function(resultB) {
            return resultA + resultB;
        });
    });
}

var resolvePromise = function($q){
  var promise = $q.defer();
  setTimeout(function(){
    promise.resolve('at finish');
  }, 1000);
  return promise.promise;
}