how to get poise?

[Coldflame]

obviously they wouldn't have put so many greatswords in a game with no poise so i'm missing how you're supposed to get it up

[Irantu]

There's no poise stat like in Dark Souls or Elden Ring. Instead this is baked into the mechanic of active blocking. Bigger weapons have a higher block stat, which allows them to absorb more damage, which is then regained through retaliation.
So instead of just eating the hit and hyper-armoring through the stagger, you block the hit and then regain the health. Obviously this doesn't work 1:1, but there are usually openings in every attack-chain.

In the traditional sense, there's a few Fable attacks that grant full hyper-armor (like the Storm Slash) for the duration of the attack.

[Tim]

Some fully charged attacks have partial poise, and Fable Arts with a cost of 3 Fable poise through most everything (I think the only exceptions are attacks that force you into a knockdown state).

Try mixing light and heavy attacks, and use fully charged heavy attacks when enemies visibly falter. The boon of heavy weapons is how easily you can shutdown enemies and make them staggerable.

And as Irantu said, they guard better. Try guarding more and waiting for an opportunity to counterattack. Once you learn an enemy, you'll find plenty of opportunities to dump heavy attacks into them and take control of battle.

[Irantu]

Also, if you're having trouble landing charged heavies without getting staggered, I'd suggest using the Booster Blade handle (the weapon is found in the chest in the poison pit in Venigni Works where the Puppet of the Future mini-boss patrols).

It scales mostly with Technique, but you can get some damage back by using a Motivity or Advance Crank. The charged heavy launches you forward quite a bit, meaning you don't have to stand right next to a boss while charging it.

[Belle Delphine Targaryen!]

No poise here.

The game is built on dodging and parrying with the latter taking precedent.