Username or EmailPassword
Umm... and THAT folks is why it is important to not teach the application, but rather teach the concepts.
That way you'll end up equally ineffective on every app. But at least you'll know exactly what is you're not able to do.
Conceptual understanding means that you can LEARN to use a specific app, but have an easier time transitioning to another app that does things differently.
But what do I know, I just teach this crap.