Experts will be along in a while. Your system clothing uses an alpha layer. The alpha layer hides your body. Look on the list of what you're wearing. Find the alpha associated with the item of clothing. Remove the item and remove the alpha. Your body which was under that item of clothing will be visible.
Take your time with this. Be patient. Read the guides. The usual progression is to move from the system avi, first with a mesh body, next a head, and finish off with a skin and hair.
Google luck and welcome back.
@TornAsunder