Bathroom Fan/Light Combo
The old one had a single neutral wire, which absolutely forced you to have fan and light on the same circuit.  

The new one has 2 separate neutral wires, allowing you the option of putting fan and light on totally separate circuits.  If you don't want to exercise the option, simply add both neutral wires to the place the old neutral was before. 

As far as the blacks, one is hot for the fan, the other is hot for the light.  Mark one of them with red tape, and wire it like the old unit.  If this has now exchanged the switches, then put the red tape on the other black instead, and repeat.