File and Folder Basics

Before you open a code editor or a terminal, it helps to be completely comfortable with two ideas you already use every day without thinking about them: files and folders. Coding just makes you interact with them more directly than clicking icons does.

A file is simply a named container of data saved on your computer's storage. Every file's name has two parts: the part you choose, and an extension — the letters after the last dot — that tells your computer what kind of data is inside.

The extension is how your operating system decides which program should open a file. Rename a photo from .jpg to .txt and the image data doesn't change, but your computer will suddenly try to open it as if it were plain text.

A folder — also called a directory — doesn't hold data itself; it holds other files and folders. Folders can nest inside folders indefinitely, which is what lets you organize thousands of files into a structure you can actually navigate.

Every user account has one main home folder — C:\Users\YourName on Windows, /Users/YourName on macOS, /home/yourname on Linux — and a standard set of folders live inside it: Desktop, Documents, Downloads, Pictures. Almost every app's save dialog, and a fresh terminal window, both start you off inside this home folder.

Downloads is worth knowing well specifically: it's where every browser saves a file by default, so it's usually the very first place to look for anything you just downloaded, before assuming it's missing.

A path is the full address of a file or folder — the sequence of folders you'd click through to reach it, written as text instead. An absolute path starts from the very top of the drive; a relative path starts from wherever you currently are.

The very top of a path is called the root — C:\ on Windows, or a single / on macOS and Linux. Every absolute path on that drive starts from there, the same way every address in a city ultimately starts from the city itself.

A file name like My Project Notes.txt works fine when you click it, but the space in the middle causes real friction the moment you type that name instead — in a terminal, or inside code.

This is why almost every real project uses lowercase names with hyphens instead of spaces — my-project-notes.txt, project-notes.txt — and avoids characters like &, #, or % that mean something special to a terminal or a web browser. It's a habit worth building before it costs you a confusing error.

File sizes are measured in bytes, but almost never shown as raw bytes — they're grouped into kilobytes (KB), megabytes (MB), and gigabytes (GB), each about a thousand times bigger than the last.

Knowing this scale helps a size number mean something instantly — a 4 KB download finishing before you can blink and a 4 GB one taking several minutes aren't a coincidence, they're a thousand-times difference in actual data.

Every time a program saves a file, imports another file, or loads an image, it's working with a path — not a name you clicked on. Being fluent with files, folders, and paths now means the next few lessons — using a terminal, and later writing actual code — will make sense immediately instead of feeling like a second new skill on top of the first.