You currently have three ways to build an APK:
At the end of June, only the second and third option will be available because the XDK build system will be retired. During that transitional period (from now until the end of June) we encourage you to get familiar with one of the other two options. The easiest of those two options is PhoneGap Build. The most flexible of the two options is Cordova CLI.
The XDK builds a standard Cordova (aka PhoneGap) hybrid mobile app, thus the app you have been developing with the XDK is fully compatible with those two build systems. The export function we are providing simply generates the appropriate build config file for those two options, other than that, there are virtually no differences between your XDK project and a PhoneGap or Cordova project.
Out of curiosity, why is XDK removing the option of building the APK within XDK? It makes it more difficult for developers as they have to use external packages to build it. I personally can't figure out how to use the Cordova CLI to build an APK with existing files, are there any tutorials?
Please read the release notes for reasons why > https://software.intel.com/en-us/xdk/docs/release-notes-information-intel-xdk#3900 < and use PhoneGap Build if you find Cordova CLI too difficult to use.