Hi. I am trying to put together a series of related social networking and teaching sites. If I want the main site never to go away, do I make it first (i.e., make it the main site)? And then if the second site may go away some day, do I make a parent copy? Thank you for your help.

I'm not sure what you mean by "never go away."

If you want site B to be a child of site A, you would have to create A first.

But, don't read too much into the parent/child relationship. Children don't inherit much at all from parent sites.

If you want to share users and content between sites, there are modules (check Snowcovered) that will help doing it.

Thanks, Joe.
It is kind of difficult to explain, but I am creating, essentially, two related religious and spiritual association sites.
Site One is my main focus and emphasis. It has more purity, but at present it serves a smaller community. My goal is to bring more people to it over time.
Site Two will serve a much wider audience. It will serve more people, but have less purity. It is kind of an 'outreach' site. It will not be able to teach all of the same things. I want to reach out to people with this site, and hopefully bring them to the other site (Site One) over a period of many years.
Eventually, once it has served its purpose, Site Two will become passe. At that point, I will deactivate Site Two. However, I will always want to keep on using Site One. Site One will probably outlive me.
If I do not want to damage Site One when I deactivate Site Two, then do I need to create Site One first? And do I make Site Two as a Parent copy of Site One? Or is that irrelevant?
I had one man telling me that I need to do Site One first, but I do not know know if that is true or not, so I thought I would check in with the experts.
Sorry I have not been taking advantage of my membership so much. I have had some other projects on my hands. If the Father wills, I hope to be able to begin taking advantage of the excellent services you offer here soon.

Personally, I would approach this by building them as two separate DotNetNuke websites, this will keep everything as flexible as possible in the future and will mean that for instance if you wish to backup a single website you can do this easily without interference from the other website.

The order of building the websites will then not matter either,

Thanks,