Remote releases can be mechanical, pneumatic, electric or even infrared and radio.

The simplest kind is just a flexible metal cable in a cloth or plastic sheath, with a button at one end and a little metal point at the other: when you push on the button, the metal bit sticks out. The sheath is generally fitted with a threaded piece for attachment to the camera.

These little doohikeys are generally used when your camera is mounted on a tripod or a stand.

Studio and macro photographers use them to avoid vibration in the camera. Wildlife photographers use them for an entirely different purpose: a camera is set up in a blind close to a nest or a den or a stream - the photographer actuates the release from a distance. Apparently, animals after a while will ignore the camera/blind presence.

Amusingly, the remote release has nothing to do with the quick release system.