For hay, which is made from grass, you merely cut the grass first. The wet grass must then be 'fluffed' with a tedder to help it dry out. Once you run over your grass with a tedder, it is ready to bail into hay. This is not as efficient, however, as the bailers only draw in from a narrow width of ground and a tedder spreads the grass/hay out quite a bit. The windrower assists by gathering a wide strip of the freshly dried hay (or straw or even freshly mowed grass) and pushes it into a narrow strip, which is much more efficient for your bailer to pick hi im farming.