When is it my turn to attack?

Source

Yeah crab is apparently incredible in PvE

>A consumable worth consuming, now that'd be a first.
Poise is built into specific armor and buffs. In past souls games, weapons would give you poise and all armors would give you some poise. High poise is like hyperarmor, where you can take hits and still perform your inputs, ignoring the hits you took. It's in Elden Ring, but you have to tailor your build for it and consume buffs.

Crab by itself won't do anything, Poise doesn't matter until you hit 60+.

Fitting.