The two words that no sentence about internet security will make sense without.
Open your phone and look at the photos. Every photo is a separate file. Every voice message, every document, every song you play - a file. The computer doesn't see "your vacation" as one whole thing. It sees a pile of separate sheets, each with its own name.
The folder is the binder where you arrange the sheets so they don't scatter. Vacation photos in one binder, work documents in another. And the binders sit in a bigger cabinet, folder inside folder, all the way up to the top level of the computer.
A file's address is simply a description of exactly where it sits - which cabinet, which binder, which spot on the shelf. When you open a photo from your phone, it knows the exact path to it, as if you told it: "this binder, this shelf, this sheet".
Why this matters outside your phone. Upload a document to email or to the cloud, and it doesn't vanish into empty space. It goes into someone else's cabinet, on someone else's computer, somewhere in the world. And from there the same rule applies - only someone with the right can reach any given sheet.
The key to the binder
I arranged files for years without thinking about what I was actually doing. Now that I build systems, I see it differently - how simple a thing a file is, and how expensive it gets if someone gets its place wrong.
All the internet security everyone talks about comes down to one question - who has the key to which binder. Understand that, and you understand half the news on the subject.