Aperture is one third of the exposure triangle and effects the amount of light entering the lens. The aperture is the size of the hole allowing light into the camera. Having a large opening in the lens will allow in more light.
The aperture impacts the depth of field of the image. A large aperture will have a shallow depth of field such that only the foreground is in focus and the background will be blurred. A small aperture will have a large depth of field and will have both foreground and background in focus. The focal length also effects the depth of field. An image with telephoto zoom will have a smaller depth of field as opposed to a wide angle shot.
Aperture is measured in F stops.
The larger the number of the F stop the smaller the aperture and smaller the hole.
Long Straight Lines
Photographing along a long straight line with varying apertures demonstrates the difference in depth of field.
I used a wide angle of 18mm while changing the aperture to display the change in depth of field.
I used a telephoto zoom of 135mm while changing the aperture to display the change in depth of field.