You must indicate where to put it. (This is the meaning of the "nocurrentpoint" error.)
Oh, you'll also need to scale the font before setting it up. The default font size is 1pt (1/72 inch) [very small]. (Not an error in itself, but an anticipated obstacle in your path.)
Since pipitas (our top SO Postscript dog) recommends a complete example here:
%! /Helvetica findfont 24 scalefont setfont %or: /Helvetica 24 selectfont 306 396 moveto %move to center of 8.5x11 page /a glyphshow showpage