If you've ever stood at the baggage claim in an airport, watching suitcases and backpacks move past you on a baggage carousel, you know exactly what a conveyor belt is. It moves the bags around in a circle.
You're most likely to see a conveyor belt in a store or an airport. It is a machine built from some material, like rubber, that's stretched across rotating rollers which pull it forward, along with whatever is resting on it. Large post offices use a conveyor belt to move packages, and your food moves along on a conveyor belt at the grocery store checkout. To convey means to move.