Gaara shapes his sand into a lookalike of himself that fights for him. Unlike other clone techniques, the sand clone's composition is usually obvious at all times, only taking Gaara's shape and not his exact appearance. Because of this, the clone can be reverted to sand at any time, most often when being attacked; as it's punched or kicked, Gaara can use the clone's sand to immediately capture the opponent's limbs. Alternatively, Gaara can use the clone as a decoy, drawing opponents to it and once they're close enough, manipulating the clone's sand against them. Whereas other clones can only take so much damage before being destroyed, Gaara can reform the sand clone regardless of what happens to it.
During the Fourth Shinobi World War, Gaara shows the ability to make a sand clone that looks exactly like the Third Tsuchikage rather than himself. In this case, the sand clone he makes exactly resembles who they're based on, not being sand-shaped lookalikes of previous depictions.