This is the most important part of any fursuit, as it makes or breaks the illusion of what you're trying to present. It can be as simple as a one- piece jumper, to something formfitting, to just using your own clothes as part of the suit. It's not unusual to watch people use bodypaint in addition to other parts.
Nicodemus' page on body, paw and head construction - http://www.nicodemus.org/fursuit/des.php
Matrice's tutorial on bodysuit making - http://www.matrices.net/bodysuit.asp
Laying out and cutting pattern
Padding, Fatsuits and Musclesuits