My mother has been expanding her horizons and has been learning more about her camera and photography in general. She’d like to wrap her head around depth of field better, so here’s my non-professional, not terribly technical explanation:

Depth of field is, generally speaking, the depth of the area that is in focus in your picture. As the aperture gets physically bigger, the depth of field gets skinnier. As the aperture gets physically smaller, the depth of field gets deeper. The trick there is to remember that bigger aperture numbers (like F16 or F22) are actually smaller physical apertures - so, bigger number, deeper depth of field.

The focus ring decides where that field, or area of focus, will be. In my crude drawing below, you see what might be the area of ‘in focus’ for something like F4 (for example’s sake - I’m not measuring here).

It’s a pretty narrow field, and something like this is often nice for portraits so your subject is in focus, but has a nice, soft, out-of-focus background behind them.

But maybe you want the background in focus. I don’t know why - maybe you want to portray a busy museum exhibit with out-of-focus people in front of in-focus artworks - but whatever the intent, you want the foreground soft and the background sharp.

So this is still F4. The area of focus is still skinny, it’s just moved to a different place because you moved the focus ring. The block person will be soft and out-of-focus, the block near the wall will be sharp. But it’s still F4.
Now, when you go to a bigger number (that is, a smaller aperture), you get a bigger area of focus.

This might be more like F22. For most intents and purposes, everything in the picture will be in focus. You still need to focus to make sure things are sharp, but exactly what you focus on is less important.

So, when you want everything to be sharp, use a big F number. (But you’ll need more light or a longer exposure, of course.) And when you’re going for an effect like a soft background or soft foreground, use a small F number and be careful about exactly what you’re focusing on in the picture.

If you’re relying on auto-focus, many cameras will let you aim at what you want in focus, press the shutter button half-way to ’set’ the focus and if you keep the shutter button half-pressed, you can reframe the picture (by moving or zooming or whatever), but keep the focus where you want it. For example, you want your portrait subject at the edge of your composition, but if you do that, your auto-focus camera wants to focus on whatever is in the middle of the composition, not your subject. So aim the camera so your subject is in the middle of the frame, ‘lock’ the focus with the half-press maneuver, and then move the camera back to the composition you really want, with your subject at the side.

Hope that helps get you started, Mom - or whoever is reading this, of course!