AR Foundation is Unity's high-level, cross platform API to support Augmented Reality. AR Foundation lets you write your app once, and build for either Android or iOS.
ARCore Extensions is a package that provides additional ARCore functionality for AR Foundation. ARCore Extensions can be downloaded and installed from the Unity Package Manager.
Requirements
ARCore Extensions requires Unity 2019.4.3f1 or later with the following packages installed:
AR Foundation 4.1.0-preview.10 or later
ARCore XR Plugin 4.1.0-preview.10 or later when targeting Android devices
ARKit XR Plugin 4.1.0-preview.10 or later when targeting iOS devices