You'll be able to use the Pig Plaza once you install it. When you put your pigs on the truck from the Pig Pen, you'll be able to choose between "Ship" or "Pig Plaza".
Pigs will be separated depending on their gender in the Pig Plaza.
Piglets cannot be moved to the Pig Plaza.
Pigs will stop growing when they are in the Pig Plaza, and the time raised will resume when they are placed back in the Pig Pen.