resolving sub-accounts to sub-directories

OK... the really hard stuff I can grasp and execute at will.
It's the simple things like creating a sub-account that will resolve to mydomain.com/sub-directory that seems like an inexact science to me. Setting up completely separate userID's with a host.mydomain.com is no problem.

Could someone go thru the steps that are necessary?
I seem to end up doing it a hundred different ways, and sometimes I get lucky, other times not.

I apologize, but I get a little confused between when to do a sub-account, vs a re-direct, vs create a WHM zone. I usually end up doing all three and hope one of them flipped the switch.

example: new sub-domain account for "forums" called (bbs)
bbs.mydomain.com => mydomain.com/bbs

preferably contain an ftp account that could be accessed as:

ftp://bbs:mypassword@mydomain.com or
ftp://bbs:mypassword@bbs.mydomain.com

Those ftp designations never work unless the host is also a system userID. I use a FTP client, but not all hosts are as fortunate.

and email:
bbs@mydomain.com or if I "have" to
bbs@bbs.domain.com

(I would prefer cpanel to create the httpd.conf server admin defaults as userID@mydomain.com), could be a system issue though.