Hi, to build for ARCore you need to enable GoogleARCore plugin and have a camera component that has “Lock to HMD” enabled. You can checkout our HelloAR sample here:
Be aware, we just have another developer preview 2 release(Release ARCore SDK for Unreal Preview 2 · google-ar/arcore-unreal-sdk · GitHub) of GoogleARCore plugin. If you want to use the latest ARCore plugin, you need to checkout our Unreal Engine repo(/4.18-arcore-sdk-preview2) and build from source code.
If you don’t want to build from source code, you can stay on the binary version of Unreal 4.18.2, but be sure to checkout the sdk-preview tag(instead of sdk-preview2) to use our HelloAR repo.