You are probably trying to apply the clothing found in the "Pose" library.  The files found in there are actually: Textures or Poses.

In order to apply clothing to a figure you go to the Figures library.  After you have applied the clothing from the Figures library, then you go to the Pose library to find the corresponding textures for that outfit.

Seeing that you are new to Poser, here is a link to a mini essay that gives all kinds of helpful information and links to "newbie"  tutorials. It's geared towards helping the new user.

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2717040&page=1#message_3095361

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi