Understanding XDM

[Christian Graulund]

Hello Guys,

I just install FreeBSD 9, and after compiling Xorg, I started trying to
figure out how to install a Window Manager.
When Following the handbook, I suggest installing XDM. I want to use
something like Openbox, as my window manager, and I can't figure out if
Openbox is a replacement for XDM, or something on top of XDM. I now there
are alternative to XDM directly like LightDM ect., but the same questions
applies to them.

So what is the function of XDM (or alternatives), and is it necessary to
have to run a WM, or DE for that sake?

Thanks
Christian G