What APKUpdater does is show you a list of all the apps that need to be updated, each one with its corresponding APKMirror link or links to other websites where you can download APKs. In other words, it will redirect you to a website where you can update your app from your browser. Once you're there, all you have to do is download and install the update.
APKUpdater is far from perfect, but it's an interesting application nonetheless. The process of updating your applications is not exactly fast or particularly easy, but it will at least make it easier to keep your apps updated.