Hey there, welcome to the forums.
I know you indeed don't want to hear this, but if you're new to C++ do nót make an online RPG.
I'm not trying to be annoying. But stop right there.
.. Stop and read this again: Do not make an online RPG.
I know all too well that it's easy to skip advice, but please do listen to this.
C++ programming is very hard at first, and starting out with networking and an RPG right away will pretty much guarantee you won't succeed at this.
I would recommend making a small singleplayer game first.
For your world question: For an RPG? A whole lot. For a simple game, not so much. Your world will be filled up with several different things: The world itself, which you sculpt, texture, fill with trees, .. and you'll probably also spawn objects through code. So it's a mix of several approaches.
But really now, make something small.