With the help of ARkit. ARkit is apple's own AR SDK.
So, what really an ARkit can do?
ARkit does use VIO (Virtual Inertial Odometry) it is just simply use to track environment and put some images into it. It uses several sensors such as Camera, Gyroscope which serves to track interest points up to later time 3D projective geometry would trace their relative positions.
Wondering where to create objects more optimize?
Well, you can use third party tools such as Unity which is the most common one. You can use Unity to create virtual objects with quite much more advance graphics.
This is an overview if you are looking for more in depth step-by-step process of building AR mobile applications with iOS. Just click here.