What is the difference between shutter speed priority and aperture priority?

It is impossible to feel different in general photography.

Under what circumstances can these priorities play their true significance?

For example, shutter priority. When you want to shoot night scenes or fast moving objects, it requires setting the shutter. Like the night scene, if the shutter is in automatic mode, it is1125 seconds, and the night scene effect is not seen at all. When you set the speed outside 1/8 seconds, and then shoot with the spleen tripod, the effect will of course be completely different.

Aperture priority and shutter priority are actually the process of normal exposure in which the shutter follows the guidance of the aperture. For example, if you want to blur a person's background, the aperture should be opened to 2.8 or even larger, or if you want to have a panoramic view and a larger depth of field, such as a big group photo or a mountain range, the aperture duty ratio should be around 1 1.

Whether shutter or aperture is the priority, normal exposure is ok, but the decisive factor still depends on where you apply it. If it is general photography, photography technology is not very high, I suggest you use the shutter speed first.