create user

hi,

    i have just created a new database. I would like to add, now, a new
user. The user can make any changes in THIS database (no one else).
    i used: (from NEW database)
        create user new_user with password "new_pass";
    i try to connect to another database with this new_user and i did
it. how can i prevent this option?

best regards,

marcos
marcos@ival.es