Part of your challenge may be that Lightroom is working WITH your operating system folder structure, so basically Lightroom is showing you a subset of the folders you have on your hard drive - those that you have associated with LR. Now, despite what else it is, LR is essentially a database program, and a database is 'an organized system of information'. If you have an address book with people's names, addresses and phone numbers in it on your desk or in your pocket, that's a database. So is a phone book. The term 'folder' goes back to the days of filing cabinets, where we had cabinets and each cabinet had drawers and each drawer had folders, and each file folder had various pieces of paper. You would think of the folder as being within the drawer and the drawer as being within the cabinet, so if you were to write those out with some sort of hierarchy it might look like this:
Cabinet 1
Drawer 1
Folder 1
Folder 2
Folder 3, etc.
Drawer 2
Folder 1
Folder 2
Folder 3, etc.
Cabinet 2
Drawer 1
Folder 1
Folder 2
Folder 3, etc.
Drawer 2
Folder 1
Folder 2
Folder 3, etc.
and so on.
So, we can replace 'cabinet' with 'drive', and no, we won't bother with why it's called the 'C' drive, and so on, but even though there's no physical arrangement the layout is basically the same. You could consider 'Drawer' to be the 'parent' or higher level of organization than a folder as it contains several folders, and you could consider Cabinet to be the 'parent' or higher level of organization than a drawer. Now hard drives are physical things as well as virtual, and so it is possible to subdivide a single physical drive into multiple virtual drives or 'drawers', but that gets too complicated so we'll simplify it by saying that we have 'cabinets' or 'drives' and we have 'folders'. Rather than having four levels of organization: cabinet->drawer->folder->files we can have virtually any number of levels - folders within folders within folders and each folder can hold files, other folders, or both.
If a folder is within a folder, it's considered a subfolder. If a folder contains other folders, it's considered (in Lightroom terms) a 'parent' folder. Parent folders can also be subfolders just as we have children, parents, grandparents, great grandparents, etc. Not so complicated.
In essence, then, rather than having cabinet->drawer->folder->files we have something like
Drive
Folder 1
Folder 2
Folder A
Folder *
File 1
File 2
Folder B
File 1
File 2
File 1
File 2
and so on. If you think of the drive as being the trunk of a tree, then each level of folder is like the branches of that tree and the files are the leaves. This is why it's sometimes called a directory tree.
So, that's essentially how your computer's hard drive is mapped out. Physically it doesn't look like that at all, but this is a convention that puts things in terms that we can make use of. Now, some folders can also have what are essentially 'shortcut' descriptions, so a path like
C: drive
Users Folder
Mike Folder
Desktop Folder
Pictures Folder
or C:\Users\Mike\Desktop\Pictures is just known as the Pictures folder.
In Lightroom, what you're seeing is the same sort of layout, but as I mentioned, it's only showing you a subset of what's on your drive because LR doesn't care about Word documents, PDF files, emails, or programs. All it cares about are image files.
When you 'import' an image, a group of images or a folder into Lightroom, all you're really doing is creating a dynamic link to that portion of the hard drive. You're telling LR to pay attention/be aware of those folders/files and to ignore everything else - non-related files/folders are of no interest to LR. But you're not actually creating anything within the LR database (catalogue file) itself, you're just highlighting a portion of what's already there. If you create a new folder from within LR you're creating a new folder in your hard drive structure, just using LR to do it for you. The effect is the same as going to Windows Explorer or Mac Finder or whatever and saying 'add new folder' and calling it whatever name you give it. When you import images into LR from an SD card or whatever, you're copying the images from the card onto your hard drive and putting them into whatever folder while SIMULTANEOUSLY creating links to those new files within the LR database. LR creates a line in it's database that says, "IMG0001.DNG is located at C:\Users\Mike\Desktop\Pictures\Mike's Images" or whatever. It's because of these 'pointers' that it's very important to always do your file management from within LR after importing images. If you move an image after importing it into LR then the link gets broken and LR says C:\Users\Mike\Desktop\Pictures\Mike's Images\IMG0001.DNG is no longer where it's supposed to be. If you have images on an external drive, say at E:\Users\Mike\Desktop\Pictures\Mike's Images\IMG0001.DNG and you disconnect the drive, LR says, "But I don't see an E: drive." When you reconnect the drive LR goes, "Oh, there it is!" and it's all happy again.
As pointed out already, every nested level of drives/folders in LR's Library module has an arrow beside it. If the arrow is pointing to the right > then the subfolders/files are hidden from view to keep things a little more organized. You can expand or collapse/contract each level of the directory tree by pressing on the arrow, and you can expand or collapse the entire nest of subfolders in any specific branch by holding down the Alt/Opt key and pressing on an arrow.
Now, because LR is working with a subset of your operating system's file structure, what you can do within LR is somewhat less than than what you can do within the operating system itself. By right-clicking or Cmd-clicking on a folder you can rename an existing folder, you can create a new subfolder by selecting "create folder inside...", you can display a parent folder not currently displayed by selecting "add parent folder" and you can remove a folder from its association with the LR catalogue. You can also move a folder from one location or drive to another by clicking on it and dragging it to a new location. Doing this within LR maintains the dynamic links. You cannot delete a folder from the drive using LR and if you delete an image or images from LR then it will first ask you if you want to remove them from the catalogue or delete them from the drive. Deleting them removes them as well, of course.
I trust that makes some kind of sense!
Mike.