Aperture-priority allows you to select an aperture manually, letting the camera’s exposure meter to automatically determine the appropriate shutter speed to result in the correct exposure. The main purpose of using aperture-priority is to control the Depth of Field.

Shutter-priority allows you to select the shutter speed manually, letting the camera’s exposure meter to automatically determine the appropriate aperture to result in the correct exposure. This allows you to choose a fast shutter speed quickly to capture action, or a longer speed to achieve motion blur