its pretty easy.
open up an existing token module (add .zip to the full filename or rename .mod to .zip) and look at its contents
you will see
1) a token folder containing the files
2) definition.xml containing simple text like this:
<?xml version="1.0" encoding="iso-8859-1"?>
<root version="2.06">
<name>Animal Tokens</name>
<ruleset>Any</ruleset>
<author>Ray Gaustadnes</author>
</root>
3) a thumbnail.png file
4) a copyright statement
You only need 1) and 2)
zip it up from the level that contains the definition.xml and rename the .zip to .mod
load it to: %appdata%\fantasy grounds\modules\