I'm not sure on the state of the GDExtension stuff just yet, but I imagine that more tutorials and examples will come out soon, once Godot 4.0 is in alpha and/or released.
I would suggest potentially asking questions about GDExtension on the #gdextension
channel on the Godot contributors chat. However, as noted here, please keep in mind that the channel is for developers first and foremost, so it may take a bit to get a reply :smile: