Photography is as complicated as you want to make it, from the simplicity of taking a photo on your iPhone to the complexity of modern sensor technology or the interaction of light with different materials. You don't need to understand everything (and I doubt anybody does), but there are some fundamental principles that will help you enjoy your photography more.
I thought I'd put together a little series of posts to explain some of the key aspects of photography in straightforward terms, avoiding jargon as much as possible or at least explaining it. So if you feel stuck taking snapshots or want to stop relying on Auto mode on your camera, I think I can help.
Aperture refers to the size of opening in the camera lens that lets light through when you take a photo. The larger the aperture, the more light gets through. So if everything else stays the same, a wider aperture means a lighter/brighter photo.
There is one more effect of changing the aperture. It also determines how much of you picture is in focus, which is called the Depth of Field. A wide aperture means a more shallow depth of field so that only things at a similar distance to your focus point will be in sharp focus. A narrow aperture means that more of the picture will be in focus. So, for example, you might choose a wide aperture for a portrait where you want the background to be blurred, and a narrow aperture for a landscape.
You might hear aperture referred to as an f-stop or f-number. Unfortunately, the numbering system is less than helpful. The smaller the number, the wider the aperture. So f/2 is a relatively wide aperture, and f/18 is relatively narrow. Confusing, but it doesn't take too long to get used to it.
One more little trick that can be useful. If you're photographing at night on a tripod, using a narrow aperture can create little star bursts from any bright lights in the scene.
So if you're using automatic mode on your camera, think about switching to aperture priority as a next step. You can start to get creative with the depth of field and you'll start to take a little more control of your image making.
This is one of the best explanations with a demonstration that I've seen, from Mike Browne on YouTube: https://www.youtube.com/watch?v=YZ-xwPegXeA