Installing cardboard deflectors (baffles) in attic
The baffles should go in between the rafters against the inside of the roof boards. They should extend from the lower soffit end, centered between the rafters, as far up as you expect the insulation to fill in. 

Your description about the existing fiberglass insulation batts seems to imply that these are installed between the attic rafters. If that is indeed the case I guess you would have to remove those before installing the baffles. If those batts are currently installed all the way up to the top of the rafters then you should remove some of that so that the upper end of your baffles are open to the cold air space where the air above the added cellulose insulation can circulate and travel out through your roof vents, gable vents and/or ridge vents.

The whole idea of the baffles is to allow for there to be a free path for air to pass from the soffit (which should have adequate vents itself) up along under the roof material and pass out through the upper area vents as described above.