Privileges (Permissions): GRAND and REVOKE

There are several different privileges a user may have for a table:

SELECT (read)
INSERT (append)
UPDATE (write)
DELETE
RULE
REFERENCES (foreign key)
TRIGGER

The right to modify or destroy an object is always the privilege of the owner only.
To assign privileges, the GRANT command is used.
Example (joe is an existing user, and accounts is an existing table): GRANT UPDATE ON accounts TO joe; The user executing this command must be the owner of the table.
To grant a privilege to a group, use: GRANT SELECT ON accounts TO GROUP staff; The special "user" name PUBLIC can be used to grant a privilege to every user on the system.
Writing ALL in place of a specific privilege specifies that all privileges will be granted.

REVOKE privileges with:

REVOKE ALL ON accounts FROM PUBLIC; The special privileges of the table owner (i.e., the right to do DROP, GRANT, REVOKE, etc)
are always implicit in being the owner, and cannot be granted or revoked.