Grant/Revoke

I'm trying to figure out what I'm doing wrong here. I have installed
pgsql (6.3.1) and set up some tables.

I create a second user, and then connect to the database that contains
those tables. As this other user, I can insert into tables without
having to be grant-ed any permissions.

I cannot figure out how to parse the output of the psql "\z" command.
It supposedly tells me who has what privileges, but I haven't yet found
any way to interpret it.

Also, if someone can point me to some documentation I would be glad to
try to help myself.

I am not subscribed to this list, so an email reply would be
appreciated.

Thanks in advance.

B.