Step one: Plug your Android into your laptop.
It will link up, and then files on your Android will appear as if they are on your laptop. You have to go to the Start Menu and then click on the 3 horizontal lines in the upper left corner. Click on the "File Explorer" option. You should see a lot of options, go to "This PC".
For me, my Android shows up as "Galaxy Tab A (2016)". Below it is "Card". This is your your SD card on your Android.
Right Click on "Card". Then, "New Folder". Create a new folder called, "Road Music" or anything else. This is what I am using to store music files downloaded from Youtube for when I'm on the road.
At this point, you have used your laptop to create a new file on your Android.
Go to "My Files" on your Android. For me, "Recent Files" is what shows up. Where is the SD card though? No where. Press Search.
The File you created through your laptop, "Road Music" should be there.
You haven't added any music yet, so your file should be empty. But, at the top left, it should say, SD card > Road Music
Click on SD card.
Now you know what's specifically in your SD card.
This is somewhat convoluted, but it does work.
As you can tell at this point, you were able to look at whatever was on your SD card when you went to "My Files" on your Android. However, it doesn't keep anything separate, your SD card files are all mixed in with your usual Android files.