How do you get in a girl's pants?
The same way you would a guy's pants. You put one leg at a time in, then pull them up and zip them. But you may look a bit silly in them, especially if they're very feminine looking.
When filming The Sisterhood of the Traveling Pants, they used 4 pairs of jeans that looked exactly alike to represent "The Pants," so that they would fit all of the girls. The girls each have different figures, which is why to portray the magical essence of "The Pants" they had to use 4 different pairs to fit them all, and to make it look "real."