New Player feeling overwhelmed; how do I learn this game.

I'm a new Diablo player and decided to jump into the deep end and pick up the game and both expansions recently, and I feel hella lost.

I'm currently still progressing through the base campaign (on expert) pretty easily with a Spiritborn right now. I'm only on Act II right now, but I'm killing things pretty easily, and feel like I have a handle on the basic skill tree and basic mechanics of the game, but I feel like there is a ton of stuff that the game has not explained to me.

I have access to all this stuff that I do not understand. Codex of Power, gem crafting, socketing items, tempering, curiosities. Not too mention there's like a million different resources/currency I have no idea what to do with? Gold, Obols, Gem Fragments, Scrolls, Veilied Crystals, etc. What should I be collecting? What shouldn't I be?

From my understanding, a lot of the games mechanics and systems aren't really used until the endgame (after the campaigns) so I know I have a ways to go yet, but are these systems ever explained? Or is Diablo just not really for new players anymore?