I have to admit, I'm as much a diablo virgin as one can be.... so your post reads a bit like
hieroglyphs to me.
What is T6 and Grift?
And your psn-id?
PS: It's a pitty there isn't a console topic, I think. Are we the only two people playing this here?
Ha ha, sorry!
T6 is Torment 6 difficulty, the highest difficulty you can choose for campaign, bounties and rifts (unlocked when you finish the game once I guess).
Great Rifts (Grift in short) have a different dynamic, which I'll explain in a second:
You play bounties first (here difficulty settings matter). During playing those, you get yellow rift stones.
In your hub location, there is Olek who stands besides an Obelisk. Activate the Obelisk by putting in a yellow stone: this opens a rift gate.
For rift, the difficulty matters. You kill monsters until a monster-kill-meter is 100%. Then the rift guardian (a boss) appears. Kill him and go back to Olek (or what this blue guy is called) to get your reward. When you play at Tornament 1 or higher difficulty, the tift guardian drops an orange rift trial stone (with an infinity sign on it).
When you have such a trial stone, activate the Obelisk with it to start the trials: several waves of mobs appear which you have to kill in a given time. At the end, you get a orange Greater Rift stone with a number in it. The number indicates the level of the Grift. The better you are (the faster you kill), the higher is the number on this Grift stone.
Now use this Grift stone to activate the Obelisk to open the Grift gate: it is similar to the rift, but two important differences: the difficulty depends on the Grift level. You have 15 minutes to fill the monster-meter to 100% and kill the boss monster at the end.
The bosses drop legendary gems. These are super powerful. You can level them up after beating a Grift boss (three tries per Grift, chance depending on actual level of the gem and Grift level).
Here comes the clue: if you beat the Grift in time, you can choose if you want to upgrade your gem...or take a new Grift stone with a higher level (the new level depends on how fast you finished the Grift).
Rins and repeat