Sea stars eat either by turning their stomachs inside out and releasing digestive enzymes onto prey or by catching drifting food items and moving them down to their mouths. Sea stars are slow-moving animals, so any prey must be similarly slow-moving or even unmoving. Many sea stars specialize in feeding on slow-moving or sessile bivalves such as clams and mussels or even on other sea stars.
Predatory starfish actually have two stomachs, only one of which is thrust onto or into prey. The second stomach receives nutrients from the digestion, where further chemicals break down the chemicals released by the first stomach. They also have a short intestine for absorption and an anus for releasing any waste.
Starfish move with the help of their tube feet, which have a large number of tiny tentacles, frequently with suction cups, on the end. They have no blood cells to help carry oxygen, instead using a simple water vascular system containing fluids that differ relatively little from the surrounding marine environment. The tube feet are moved by pumping some of the fluid from this water vascular system into them, essentially inflating them. While the feet do have suction cups on the end for adhering to rocks and other surfaces, they also excrete chemical adherents.