You're welcome!
It makes sense to want to know everything about it. That said, it's not
required to know
everything and you may have more enjoyment from getting the main things right and learning "extra" stuff later on
Basically, what I'm saying, I think, is that if you understand vertex array (or using your own vertex data) then you'll have pretty much all scenarios covered. You may never need the vertex buffer (it's a recent addition and I still haven't had the chance to use it!) but it's there if you do need it.