Aperture (also known as your f/stop) describes the actual size of the opening of your lens when a photo is taken. The more open your aperture is, the more light is let in your camera and the brighter your image will be. The lower the f/stop, the wider the opening. The higher your f/stop number is, the smaller the opening will be. It’s easy to remember if you think in terms of opposites:
low number = more light high number = less light.
Aperture also affects your Depth of Field. Depth of Field is how much of your image is blurry or out of focus. The lower your f/stop is, the more blur you’ll have in your background. The higher your f/stop is, the more of your background will be in focus and sharp.
low f/stop = more blur high f/stop = less blur
The examples below show that with a smaller f/stop, the more blurry the background will be.
If I am taking a portrait of a child, I prefer to use a shallow depth of field. One, because I love the way it looks, and I like when the focus is completely on their expression or personality, and less about the sometimes distracting background behind them.
It takes some practice to get use to these settings. Just remember, the lower your f/stop = more light & more blur, the higher your f/stop = less light and less blur!! Turn your main mode dial on your camera to the letter A (nikon) or Av (canon) to practice shooting on Aperture Priority. You'll chose the f/stop number and your camera will do the rest for you! This is an easy way to learn aperture and how it changes the look of your photos, without having to try and shoot in full manual mode.