Lots of files & sanding, like any stem. Acrylic is harder than other materials, so it takes more sanding to shape. But it polishes up a lot easier.
As far as drilling an Acrylic stem. . .you could just drill through, then put an indentation at the bit using a Dremel. But, really, you might as well just buy a pre-molded stem if that's the plan.
Really getting in there and creating a deep V-slot can be difficult with Acrylic, because it's so hard, but it's important. Use a 1mm drill bit to drill, then fan the slot open. Then lots of work with files or thin saw blades.
They bend the same way Vulcanite/Ebonite stems do.
But they require higher heat. And have a much shorter window where they're pliable after heating.
I use a heat gun. A hairdryer would work, too.
Or a flame of some sort.