Pieces such as those found in the Basic Pieces and Basic Shapes categories of the Furniture Album and Party Gallery are generally used to create other pieces of furniture. You will find an explanation of the techniques involved creating such basic pieces in the Draw Menu documentation. There are also a number of videos available that explain the basics of furniture creation.
VLINE and HLINE are vertical and horizontal lines. VPLANE and HPLANE are vertical and horizontal planes. RUG and PIC are pieces generally placed close to a wall, floor or solid object for decoration. ICON is a straight line used to embellish the icon of a new piece ---- it does not show in 3D views. VPATCH and HPATCH are invisible vertical and horizontal planes that can be used to block unwanted lines from appearing in 3D views.