Time Machine capabilities

Would appreciate a bit more detail about the process. The files that I want to backup using Time Machine are on an outboard HD, not on my Mac's native HD. I want to back these up to another outboard HD that I can use as a backup disk. This latter step -- choosing a backup disk -- is easy. However, the first part is not. So ....

How do I get Time Machine to recognize the first external HD as the source of the files I wish to backup, rather than it trying to automatically backup my Mac's HD?

Well, I spoke too soon. I have attempted to back-up the external HD with my music files to another external HD twice now, with unsatisfactory results, i.e., when I click on the the back-up folder created in the process to open it, I get an application "Terminal." "Terminal" (aptly named) doesn't open the folder, it just gives me a lot of extraneous information about encrypting, working with "shells," etc.

How do I get the back-up folder to open up normally (as with all my other files), and avoid this "terminal" conundrum?

Actually, I've appreciated your efforts to help, but none have succeeded. So, I've simply moved the files onto the external HD for back-up (this will take ten hours). My desire to use Time Machine was to speed up future back-ups (since, theoretically, it would only copy new files each time), but this became more difficult than it should have been with the introduction of the unix app, Terminal, into the process for inexplicable reasons.

Thanks.

There is some confusion here, so let me try to explain. I was not planning on using "Terminal" at all, and was completely unfamiliar with it. I only became acquainted with it when I tried to open the backed-up folder of my music after using Time Machine. Instead of simply opening, like a normal folder, when I clicked on the folder, it opened Terminal but not the folder. And, no amount of attempted work-arounds has succeeded in opening the folder.

There is obviously something involved in Time Machine -- in this particular instance of not backing-up my computer HD, but accessing an external drive -- that is dictating the involvement of Terminal. I know this because I have gone through the laborious process of simply copying the files to the same HD in the past, and had no problem or involvement with Terminal.

As I said, I wanted to try to use Time Machine to speed up future backups, because it would only copy new files on the later backups. Can't figure this one out, so I'm going back to simply copying from the desktop and not using Time Machine at all.

Thanks again for your attempts to help out.

Thanks. That's what I needed to know. Backing up now.

Well, no, that doesn't work, either: "should" being the operative word.

Let me try another approach: are you familiar with the application "Terminal"?