I’ll help make a practical use tutorial later if there is no tutorial later. We still need to wait until all targets get Native Extensions support. I was personally waiting on that to really use it. Sounds like it’s happening within next few weeks!
For majority of users, you will probably never develop your own Native Extensions and instead use the generic ones already made, because majority of a game can be accomplished without them, and there are only so many reasons most devs would want extra features such as implementing 3rd party 3dks for ads or using target os api /hardware features which are not already implemented in vanilla Defold engine.