Hard drive full, missing RAW images

I'm pretty new to Lr and have had a lot of issues.  I've read and read for hours and hours and days and days and have only run across a hundred ways to do something, which hasn't helped me so far, and my HD is so full very little works now.

In a nutshell:

When I open Lr now EVERYTHING says that the original file is missing.  I've no idea why this is since I've not moved or renamed anything.  I honestly have NO idea what's going on, but I've spent all my time trying to fix this issue, rather than shooting and working on my photos.  Productivity has come to an abrupt halt.

I've tried to use the option where you find the missing file, but even doing that... isn't working.

When I go into my HD location, USERS, my name, and then PICTURES... the  folders "Lightroom"  and "2017" are there.

In the folder named "2017" is another folder named "2017-07-27," and inside THAT folder is a bunch of images (NEF and JPG) and their corresponding XMP files AND yet another folder titled "2017,' and inside THAT folder is 5 other folders with dates.

The folders within folders with images and more folders etc confuses the heck out of me, but it 'appears' all the images and files are inside all of those folders, and I've NO clue what to do with them at this point.  Lr will SEE the images when I choose that location on the left panel while viewing.  Maybe I'm misunderstanding what I'm supposed to be looking at etc., and maybe those previews from the import from my camera (I don't have a card reader) have been auto-deleted.

My BIGGEST problem at the moment is that I BARELY have enough space on my computer to do anything, and that's no exaggeration.  I get low disk space in Lr and the program won't allow me to to even shut it down.  I have to literally restart the computer to get Lr to shut down.

I've been reading for days on end about how to get all those image files and corresponding XMP files to my external drive and have, as mentioned before, only become more confused by the conflicting information out there.  And most of the info is for much older versions of Lr.

Even though I deleted a lot of stuff off my MacBook Pro... I have even LESS storage space now than before I deleted things, which I also don't understand.

How on earth do I solve this problem before my HD ends up crashing or locking up completely?

How do I get the actual RAW images off my local HD and onto the external asap and make it so Lr is able to SEE them?

Oh, I also copied the image folders onto the external to see if I could even import them from there, and Lr just doesn't want me to do that.  So, I'm not sure what to do.

ANY help in solving this would be a Godsend as I've not been able to do anything in days other than keep researching and reading a million different ways to do this, most of which isn't working.

Thanks in advance.