I finally got how to su - in my mac from the terminal. Now I would like to be able to add new users. useradd -m -d ..... doesn't seem to work.

This being a Linux forum, not an Apple OS X forum, you might be asking the wrong group of folks.

I'm aware that OS X is based on Unix via BSD, but I have no way of knowing how many of the commands are the same as what Linux has in a standard installation.

Try
and see if there is a manual page for the command. If not, you may not have it on your system.

If not, there is also "adduser"
http://linux.about.com/od/commands/l...l8_adduser.htm

If that doesn't work, try an OS X forum where people are familiar with Apple.
Good luck. With some research, I'm sure you'll learn command line basics for your system.

Well just a little googling I came up with This.

Also here is a list of OS X COMMANDS