Giridhar, from the context, I assume that you are somewhat new to the 3000.
It seems that you * might * need to become aquatinted with accounts and
groups; I'm not sure. And help on NEWDIR is not casual reading. There are
other resources, such as running POSIXCBT.LSN.SYS, which is meant to explain
POSIX features to MPEers, but can be used the other way. And within help,
there is helpstudy, which actually starts spends the first ten screens
explaining what a computer is (!), and is somewhat dated, but does get
around to explaining MPE concepts. That is casual reading.

I have had to undo the results, when our Oracle DBA used mkdir. It took
three days from start to finish to coordinate the work among the involved
and the affected parties. There are two reasons why this might be concern.
First, in our shop, we use private volume sets. If you do not, then at least
that will not be a problem for you. The second related reason is, unless the
directory is under a group, which by definition is under an account, then
the directory will be on the system volume set. Among ways to tell is to
issue the command "dstat all". Under the header, you will get several lines
much like this:
  1-ST32550     MASTER      MEMBER1         (MPEXL_SYSTEM_VOLUME_SET-0)
If that last column always contains MPEXL_SYSTEM_VOLUME_SET, then you don't
have to worry about this, and the rest of this is not a concern. If any of
them contain anything else, then you have private volume sets.

The next consideration would then be why and where you want to create an
entity to contain files. Some elements in a 3000 such as the line editor do
not like to use POSIX or HFS names, and putting their files anywhere besides
a group would keep them from being useful. Just to make it confusing, there
is some overlap. For example, say you have a set of COBOL source files in
/APP/SOURCE (POSIX / HFS naming), or .SOURCE.APP (MPE naming). If you are in
SOURCE, and issue newdir ./PROJECT, you will get /APP/SOURCE/PROJECT, and
there is no "MPE" name for this.

If you are using private volume sets, and want to create a sibling of
SOURCE, you would need to know that volume set it is on, by issuing
LISTGROUP SOURCE.APP. The resulting listing will include a line for HOME VOL
SET. If it reads HOME VOL SET : DEVELOP, then you would need to issue
NEWGROUP PROJECT;HOMEVS=DEVELOP
and
NEWGROUP PROJECT;ONVS=DEVELOP