Move the item from the library onto the figure onto wich you want it to conform.
Keep the mouse button pressed until you see "Add and Conform" - this might take a few seconds if the library is still filling (after you start PoserPro). Then release the mouse button. After the library has filled it goes a lot quicker
If the item is autoconforming, you don't need to check any boxes. If is not you might need to check the Include morphs checkbox.
Be sure you drag the item onto a body part which is not covered by a clothing item since it then may conform to that item instead of the figure

This is how it works for me