SELECT ... FOR UPDATE ...

I looked through the documentation and attempted a search of the mailing
lists (one can submit a
search but never returns). I also looked at the titles of the sql
mailing list for the past year, but can
not find an example usage of the SELECT .. FOR UPDATE query.

Could someone please give me an example of how it is used. Does it take
two statements, the
SELECT ... FOR UPDATE statement followed by another UPDATE statement? or
does one
somehow do an update within the select statement.

Thanks.

Richard