I will preface this by saying I havnt played a game yet but I have watched several battle reports in prep for my first game but I am very confused with the proper method of building the attack pool.

With the rules the way I understand it is: storm troopers with A dlt19 in the squad have two options. A. 4 white and 2 red. Or B. 5 white

my confusion is that I see players rolling what seems to be an ridiculous amount of dice some times from Corp attacks. I just want to make sure I understand the rule before I play.

You are correct. If the unit is also upgraded with an extra trooper it could roll an additional white die.

Are you sure it is stormtrooper units that are rolling a ridiculous amount of dice? Rebel Trooper units with a z-6 heavy and extra trooper can roll 5 black and 6 white dice in a single attack. 11 dice does seem like a ridiculous amount.

It might have been. It just seemed like an over the top amount. As long as I understand the rules I am good.

Having been on the receiving end of those 11 dice (or worse, 12 black dice when I wasn't smart enough to run from an AT-RT with a flame thrower) I can assure you it is a ridiculous amount of dice haha. lesson learned for the future.