That depends on where you are coming from. If you are using Godot 3.2 stable then you just need to set "Hand Tracking" to "optional" in the Android export settings.

As for the code for using it there are a initialization steps you have to do in your main scene. I suggest you take a look at the hand tracking demo in the godot_oculus_mobile plugin (https://github.com/GodotVR/godot_oculus_mobile)

However, if you are using an older beta release of 3.2 then I suggest upgrading to 3.2-stable because the packaged apk in the export templates does not have to correct permissions to support hand tracking.