User permissions

I created a user and I want to give this user access to a portion of my files in my account. I create the user and assign the rbash. The user though cannot create anything because the user and group is my ID. So I issue the following command hoping that the new user ID will be added to my group. Well, the new user cannot create files because of the permissions. How do I set the ID to be able to create files?

Thanks,

hello, please stop using tools - mostly (bad) shell-scripts - you do not
know what they do.
just TRY to learn unix, its easy! and do it by hand, tomorrow you
perhaps are on a system w/o that tools
on bsd you have in /etc two files: passwd and groups
edit passwd, duplicate the line of user A
on the duplicated line: change A by B, change user-id (and home-dir)
in groups, add to group A the user B
thats all, two files, sure you can edit a file !