How is the GPIO adapter supposed to work?
I installed the Add-On, added new button and the button should appear to where? It isn’t on the Things page.
The documentation is really poor.
It would appear when you click the + button on the Things page. I believe the GPIO adapter may be broken at the moment, though.
Yes, nothing comes up with the + button. I’ll wait for the fix then 
With the GPIO adapter you first need to tell it which pins the adapter should be controlling.
Goto Settings->Addons and then click on the Configure button for the GPIO adapter.
The clicp the + under gpios and fill out the pertinent information. Click + again to add an additional GPIO pin. Click the X to remove a GPIO pin.
Then click Apply. Now when you click + in the Things screen you should see new devices to add (using the name you entered in gpio configuration page)
It is working now, thanks!