Creating a file and saving it stores your work with a name and location. Opening a saved file brings it back so you can continue working. Saving regularly prevents losing work.
Open a word processor, create a document, type text, and save with a clear name. Close and reopen the file. Experiment with saving in different locations.
When you type into a word processor or any other application, your work initially exists only in the computer's RAM (random access memory) — a fast, temporary workspace that is erased the moment the program closes or the computer loses power. Saving a file is the act of copying that temporary work from RAM to permanent storage — your hard drive, SSD, or a cloud service. Until you save, your work is one power outage or crash away from being gone forever. This is why saving frequently is a fundamental habit, not a minor courtesy.
Creating a file starts a new blank document in an application and adds it to RAM. At this point, it has no location on disk and no name. When you first save with File → Save (or Ctrl/Cmd+S), the application asks you to choose a name and a location — a specific folder on your computer or in the cloud. From this point forward, that name and location define where your file lives on disk. The file extension (the part after the dot: .docx, .pdf, .xlsx) signals what kind of data the file contains and which applications can open it — knowledge you bring from understanding file types.
Opening a file is the reverse process: the application reads the data from the file on disk and loads it into RAM so you can work with it. You can open the same file in multiple sessions — each time, the stored version on disk is loaded fresh into memory. The crucial implication is that changes you make after opening don't automatically flow back to disk; you have to save again explicitly to update the stored file. The file on disk only ever reflects the state it was in at your last save.
Keyboard shortcuts make saving fast enough that you can do it reflexively. Ctrl+S (Windows) or Cmd+S (Mac) saves immediately with no dialog if the file already has a name and location. Ctrl+Shift+S / File → Save As saves a new copy under a different name or location, leaving the original unchanged — useful when you want to make a variation without overwriting your current version. Many applications now include autosave (Microsoft 365, Google Docs), which saves to the cloud every few seconds automatically, but even these have limits: autosave may not capture your last few keystrokes after a crash, and it requires an internet connection to function. Building the habit of manual Ctrl+S saves protects you even in applications without autosave.