Location of files: Main Storage versus SD card

Question

I'm trying to figure out what is stored where on my Android phone (an unrooted Samsung Galaxy S8 with an SD card).

I can examine the phone's contents either via any of the several file manager apps I've installed, or by mounting the entire phone as a network drive on my Windows 10 machine.

My File Manager App shows me the contents of "Main Storage" and the contents of "SD Card".

The contents of "Main Storage" show up on the network drive in a directory called /sdcard. The contents of "SD Card" show up on the network drive in a directory called /storage/0000-0000 .

This is very odd, since the directory called "/sdcard" on the network drive is the opposite of the directory called "SD Card" in the File Manager app.

The File Manager app shows 57 gigs total in "Main Storage" and 256 gigs in "SD Card". This suggests to me that the former is the phone's built-in memory and the latter is the actual SD card. But I'm thrown for a loop by the fact that the former is called "/sdcard" and the latter is called "storage/0000-0000", which seems backward.

I could, of course, pull the SD card out of the phone and examine its contents directly on another device, but I'm squeamish about handling the card. And no matter what I learned, I'd still be curious about the odd naming conventions.

So:

Question 1: What's going on? What's in which directory?

Question 2: If I want to back up all of the data (but not the system files or software) on my phone, does it suffice to make copies of /sdcard and /storage/0000-0000, or are there other places data might be stored?

Additional Info: The App X-plore confirms the odd naming, in that it shows me two directories, one named both "Phone Memory" and /sdcard (it shows the former in bold and the latter in roman, both labeling the same directory) and another named both "SD card" and /storage/0000-0000.

Answer 1

What's in which directory?

/sdcard is the so-called "internal SD card" (internal-sd, on "internal storage" and not physically removable without breaking the device, hence also referenced as "Main Storage" in your case), while /storage/<card_id> is the physically removable external-sd.

are there other places data might be stored?

There are. Without root, you e.g. won't have access to where your apps store their data (/data/data/*). To perform a real full backup, you'd need a custom recovery like twrp to perform a nandroid backup. The closest you can come to that is adb backup – but even an "adb full backup" is incomplete (especially as apps can "opt-out" of that, so they won't be backed up by adb backup).