Getting under the ball at release

Can someone please explain to me what getitng under the ball at release means because i need to know before i try and throw a sinker.

only certain arm slots and wrist positions at release can produce a sinker

e.g. a sidearm pitcher will hav more sink than sumone throwing overhand, but an overhand pitcher will get 12-6 curve on his curve

im lucky to be able to get tons of sink on mine - i throw low to medium 3/4 but hav a weird wrist position at release which causes everything i throw to move… even when trying to get it to go straight… so if it doesnt work it more than likely will never work

how do u throw your sinker?

i just hold the ball like a 2 seam and put my 2 fingers together on the leather inbetween the seams then throw