Hello, this outfit is a dForce item. it is intended to be used with DAZ Studio's dForce system.
In a nutshell:
Drag and drop the dress on G8F. Morph and pose her as you like.
In the scene tab, click the Dress
Click the surfaces tab and select all the parts of the dress.
Click Simulation. Click the Blue Simulate button.
Wait a bit while DAZ Studio drapes the dress to G8F's current shape and position!

if you are unsatisfied with the pose or morphs, Click Choose the Dress and click Clear (under the Simulate button) and the simulation will be removed from the dress. Click Edit > Figure > Zero > Pose & Morph to return G8f to her default self.

;>

Andy!