The Bio Generator is a generator added by Forestry. It is an Industrialcraft2 compatible generator and can be used to power machines introduced by IC2. It has a ten bucket fuel capacity and will burn one bucket of biofuel in one minute and forty seconds, producing 32,000 EU total. If you have an MJ/RF system it's arguably a better idea to use MFR's Biofuel Generator instead.
To fuel this unit, simply open it up and place a can, bucket, or cell of Biofuel or Biomass inside. Alternately, route a Waterproof Pipe or Liquiduct to the device.