The crosses are called "body handles". If you click on one you will find that you can drag it and use it to pose the skirt. The skirt will not automatically move with the figure's pose; you have to pose it by hand. Do not mess about with parenting the skirt ; just conform it, pose the figure, then use the handles (and any morphs) to pose the skirt. (I'm not quite sure what effect trying to conform AND parent the skirt will have- could be messy!).

  You will find that virtually all conforming skirts and dresses use body handles of some form, though the symbols representing them vary. Look for a piece of detached geometry below the clothing.  Once selected you can also move them using the dials.

Before P5 introduced dynamic cloth it was the only way to create a skirt.

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