Getting Started with ARKit
First things first: Augmented Reality is an inherently 3D activity. The ease with which you pick it up will be directly proportional to your existing experience working in 3D. This is not to say someone without 3D experience can't do AR, but it will be harder for you until you become more familiar with common 3D principles. The skill set used for creating 3D games and AR experiences are essentially the same.
If your'e a complete 3D noob, I suggest checking out some of the RayWenderlich.com tutorials on getting started with 3D game development.
Step 1: Choose your IDE
The first decision to make is whether you want to use Xcode or a 3D game framework such as Unity or Unreal to create your experience. For the purposes of this guide, I'll assume you will choose Xcode, simply because I have no personal experience with the other two options. If you're already experienced with one of them or are feeling adventurous, then I'm sure you can find AR learning resources online.