If you are using Pub 2003, then go to Tools > Web Page Options, where you
can enter a Description and Keywords.

If you are asking how to "optimize your site for search engines", then that
is an open ended conversation. Perhaps go to Google, and read about how to
optimize your site for Google:
http://www.google.com/webmasters/

And then use Google to search for other articles about "optimizing your site
for search engines"

DavidF