Latex has a mechanism that makes it easy to add in new commands or
change something,  called style files.  You can tell latex what
style files to include by using the line

      \usepackage{stylename}

in the preamble of your document, like so:

      \documentclass{article}
      \usepackage{doublespace}
      \usepackage{epsf}


doublespace and simplemargins are both style files.  You can find them
(and many others) in subdirectories under /usr/athena/lib/tex/macros
as doublespace.sty and epsf.sty.  

If you want to use a style file that exists someplace else, you have two
options:

- Copy the files into your home directory, or whichever directory you
  usually run latex in.  That way, latex will be able to find the file.

- You can tell latex where to find these new style files.  To do this,
  you need to modify the TEXINPUTS environment variable.  In your
  .environment file add the line:

	setenv TEXFONTS .:/usr/athena/lib/tex/macros

This tells latex to look where it normally looks. Now add on the
directory where the style files you want are, for instance if you want
to add /mit/consult/lib/tex/macros you would have:

setenv TEXFONTS .:/usr/athena/lib/tex/macros:/mit/consult/lib/tex/macros

In this case you would also need to put 

	attach consult

in your .environment file so that the directory would be accessible.

Now to use the .sty file, just put its name in a \usepackage command.