Can somebody help me understand the concept of an OU. How do I join a server
An OU (Organisational Unit) is part of a hierarchical structure like a
directory tree. (Some confusion with directory referring to file
structure and with directory like in AD.)
You may join a server to a domain, not a OU. But you are allowed to
move a computer object within the AD from one OU to another. You may
want to do this to take advantage of different GPOs assigned to the
various OUs you may have.
The concept is quite different from "old" NT 4.0 domain. In NT 4.0 you
have a flat structure, in AD you have hierarchies and enheritance. You
are able to map a company hierarchy into AD (or not, but this is
politics).
Ciao, Walter