The user-defined pager allows you to look at a file without having to leave Arcgsh. It is not a built-in function of Arcgsh. Instead you are free to choose a ``pager program'' which actually displays the file. (I use and recommend the public domain program LESS.TTP by Moshe Braner.)
When you select the ``Show file ...'' menu item from the ``File'' menu the GEM file selector box appears and asks you for the name of the file to be shown. If the pager program has not yet been selected a dialog box appears to let you do so (see description of the ``Configuration'' menu).