When you make something on a computer—like a document or drawing—you need to save it to keep the work permanently. Saving puts your file in a folder where you can find it later. You can then open the file again to keep working on it or look at it.
Have children create something in a program, then save it using Ctrl+S or File > Save. Give it a name and choose a folder. Then close the program and open the file again.
When you draw a picture or write words on a computer, that work lives temporarily in the computer's memory — like holding something in your hands. The moment you turn off the program or the computer, that memory disappears, just like dropping what you were holding. Saving is the act of writing your work permanently onto the computer's storage, like putting it into a drawer where it will stay even after you walk away.
You already know what a file is — a container that holds your work — and what a folder is — a place to organize files. Saving connects these two ideas: when you save, you give your work a name (that becomes the file name) and choose which folder it goes into. The program writes your work into that folder as a file. From that moment on, the file exists independently. You can close the program, restart the computer, or walk away for a week, and the file will still be there when you come back.
Opening a file is the reverse process: you tell the computer which file you want, and the program reads the file's contents from storage back into memory so you can see and change them again. The two most common ways to open a file are through File > Open in a program's menu (which lets you browse for any file) or by double-clicking the file icon in a folder (which opens the right program automatically).
The most important habit to build is saving frequently while you work. Many programs let you save with the keyboard shortcut Ctrl+S (or Command+S on a Mac) — pressing it takes less than a second. If you save every few minutes, the worst that can happen in a crash or power outage is losing a few minutes of work. If you forget to save, you can lose everything. As you get comfortable, you'll also learn Save As, which saves a copy of the file under a new name or in a different folder — useful when you want to keep two versions of the same document.