There is also some new stuff introduced to the game while you were gone, somethings to look out for are Legedary Gems and Kanai's Cube, both of which are used for the augments you mentioned.
That should get you started, most of the old stuff is still the same, set bonuses are a whole lot more usable (required) now.
Other than all that, Welcome back and hope you enjoy the game
2
Learning all of the stuff is going to take some time, but I can give you a few places to start.
Icy Veins: Beginners guide to seasons
A general overview of the current season from Blizzard
The season journey, Which is a sort of sidequest to progress alongside greater rifts. And the reward you gain from completeing the chapters in it.
There is also some new stuff introduced to the game while you were gone, somethings to look out for are Legedary Gems and Kanai's Cube, both of which are used for the augments you mentioned.
That should get you started, most of the old stuff is still the same, set bonuses are a whole lot more usable (required) now.
Other than all that, Welcome back and hope you enjoy the game