Property links: one layer follows another
A link makes one layer's number follow another layer's, so it moves without keyframes of its own.
Try this
- Press play. The blue shapes have no keyframes; each one follows another layer.
- Right-click a follower's linked Position field in Transform, choose Edit link…, and change Layer.
- To make one, right-click a Position field, choose Pick-whip to a layer, and click the leader.