Position the object, take a frame, move it fractionally, take another. Played back in sequence the object appears to move on its own. The technique is as old as cinema itself and spans clay animation, puppet work, cut-paper, and pixilation, where human performers are the objects being posed.
The labour is the defining fact. At 24fps, one second of finished animation means 24 individual poses and exposures — a feature film represents years of work. Many productions shoot on twos, capturing each pose for two frames, which halves the workload and produces the slightly stepped motion characteristic of the form.
Technically it demands absolute stability: locked camera, manual exposure, manual focus, and constant lighting, since any drift flickers across the sequence. Onion-skinning tools that overlay the previous frame on a live view make incremental movement far easier to judge. The imperfection is much of the appeal — the visible handmade quality is precisely what audiences respond to.