%!PS
/Courier             % name the desired font
20 selectfont        % choose the size in points and establish
                     % the font as the current one
72 500 moveto        % position the current point at
                     % coordinates 72, 500 (the origin is at the
                     % lower-left corner of the page)
(Hello world!) show  % stroke the text in parentheses
showpage             % print all on the page