What is aperture?
Aperture is the amount of light being admitted through the lens as you capture your subject.
How can you tell how much light that is?
In the example image, the aperture, also known as the f-stop, is the number 4.5 (F4.5).
Adjusting the aperture allows you to get creative. Think of a crisp, focused image (foreground and background), compared to a focused foreground subject but with a blurred-out background.
Using an aperture of f/4.5 compared to f/16 helps create the blurred background effect. Dialing in f/16 gives you more of the postcard type creation.
What is going on?
Your camera lens has what is called a lens diaphragm and it consists of overlapping blades. When you (or your camera in auto) change the aperture setting, you cause the blades to close-down or open-up.
At f/16 the blades close-down creating a smaller opening for light to enter, think postcard effect. In comparison, a setting of f/2.8 (or f/4.5) opens up the blades allowing additional light to enter. Think focused subject, blurred background effect.
Have you found the aperture display on your camera if you were not familiar with it before now? If you have, great!
If you are having trouble feel free to contact me and I'll do my best to help you figure it out.
To learn more about aperture and how it affects your photos, I invite you to check out my book, which is full of easy-to-understand photography tips.