Once you've moved off 'Auto' to shoot on the 'Aperture' setting, I found I could artificially force the aperture setting to be higher or lower than the camera was telling me. On my camera this is called 'Exposure Compensation', a small button that I push down and hold, on top of the camera. I've found it particularly useful for shots involving bright light like snow on sunny days, or sunrises.
So if you move onto the Aperture setting on your camera, you can then use Exposure Compensation to experiment with forcing the exposure to be slightly lighter or darker than what the camera wants to tell you, a useful trick in some situations.
I found yesterday's post particularly hard to write. It's hard to articulate, even for myself, getting beyond 'Auto' without making it too complex. But if you're in the same position I was in, trying to do that, there is some technical info that may help.
Shutter speed and aperture are two opposite settings on the camera. Shutter speed is shown on the window of my camera as a fraction, like 1/125; aperture is shown as 'F Stops', like F3.5 or F16. Trying to understand these in theory just baffles me, but learning how they impact the picture through practice comes easily. For example, if you take a picture of a scene, 1/125 will normally give a sharp picture, but 1/8 will not; you just can't hold the camera steady enough. And if you want a picture of something moving quickly, you might want 1/1000 or higher to freeze the action. This seems like common sense to me.
If the shutter speed is faster, the aperture must be lower to let in enough light; if the shutter speed is slower, the aperture must be higher to avoid over-exposure. In the Auto setting, the camera balances these. In Aperture setting, you set the aperture, and the camera choose shutter speed; in Shutter mode, you set the speed and the camera chooses the aperture. But in all cases the camera still automatically tells you what the exposure should be, using the built-in light meter. Exposure compensation lets you over-ride the camera a little to make the picture lighter or darker.
Mid-range settings are usually no problem either way; it's the extremes that cause you to stop and think about the settings more carefully - like photographing waterfalls, which I'll discuss tomorrow.
You might want to know that I use a Nikon DSLR, the lowest most basic model that was available at the time, the D3000; my wife's camera (which I also sometimes use) is a Canon PowerShot, a higher-end point and shoot model.