Aperture is a opening lens that takes in the amount of light and hits the camera sensor. when the aperture is wide open means that more light it passing through so it blurs out the background. The good side of having it a wide aperture is it the possible light because it focuses what you want on the object but blurs out the background.
Aperture when its at smallest means that less light passes through to the camera sensor. The only times you use small aperture when there is a lot of lightning. Also has a slower shutter speed.
examples...
The reason haven chosen these photos is an example of how aperture works. I have picked two photos to explain why i like them both, i most like the first one the bird sitting on the branch because of the colours. It is on small aperture because the background is blurred and just focusing on the bird and the branch.