first ad all the users  through ur portal site
settings, and remember first of all users will have
the same rights as they have now when u added them and
gave rights to them, rights are inherited from parent
areas, in ur case it will in herited from the portal,
now go into each area and there will be a link on the
left bar called manage  security, there add the user
with the user  name and give each user there own
rights, in case here u can mak e agroup and give them
rights, like im my case there is an area where
students have different rights then teachers, i hope i
have solved ur problem