Maybe I wasn’t being clear enough with my question. I’m just trying to get a better understanding of how MSM works, given my setup, so I’d have an idea of how to proceed.
Specifically, I’d be interested in installing whatever files MSM needs to run a second site inside a subdirectory of the main website’s root. The instructions for MSM Creating a New Site Step 4 reads “Set up public access via a sub-folder, sub-domain, or domain.” That’s not very detailed, and there’s a number of ways this step can be done. So I explained my setup, in the hopes of getting a little more detail with step 4 ... simply as guidance, since I’ve never used MSM before. I don’t think this thread is out of the scope of Technical Support.
Anyhow, I found an article written by Chris Arnold that addresses some of what I’m looking for, although it appears to be written for EE1 (whereas I’m using EE2). I’ll review his notes and do my own trial and error.