Basically it uses fuel to pump fuel. We have a couple different types of motive flow pumps in my jet: ejector, and turbine. Ejector motive pumps use the venturi effect to transfer fuel, using high pressure motive flow
Turbine type motive flow pumps use that same high pressure motive flow to drive a turbine which moves fuel from one tank to another.
In general, motive flow is used in fuel transfer between tanks in an aircraft. They are lightweight and relatively simple systems in comparison to using mechanically driven transfer pumps at all the tank interfaces. It is all the same fuel being used for engine feed, and motive flow, but fuel that isn't being consumed is regularly cycled through the motive flow circuit, and then back into the tanks.