While in aperture priority your camera decides what aperture your camera will be depending on your lighting and other factors. when in exposure priority you will not have control of your exposure your camera will automatically set that. if you are in manual mode you have control over everything, the exposure, the ISO, the shutter speed. You control every function of the camera and how it shoots.
This is what the setting for aperture priority looks like on a Canon camera.
this is what shutter priority looks like on a Canon.
this is what manual looks like on a Canon and Nikon.
this is what aperture priority looks like on a Nikon.
this is what shutter priority looks like on Nikon.
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