I’ve been explaining recently why you might shoot in Av (Aperture Priority) or Tv (Shutter Priority) mode.
Sometimes it can be hard to understand these things so I’ve found a cool tool you can use to see how these interact. Click here to visit the hands on simulator.
The simulator is an interactive camera that you can use online to experiment with aperture and shutter speed. You get to set the speed and the aperture and take your shot – the preview shows you what the image will look like with those settings.