Inspect the bottom of your window air conditioner for the type of drain installed. Some air conditioners will have a standard hose adapter so you can thread the hose in place. Others have a ribbed plastic shaft designed for sliding the hose in place.
Thread a water hose onto the hose adapter, or cut the hose adapter off the hose with a utility knife. Slide a band clamp onto the hose, and then slide the hose onto the ribbed plastic shaft. Slide the band clamp over the plastic shaft and tighten it with a screwdriver.
Unroll the hose so the end of the hose goes downhill. The land around your home is graded to route water away from the house. For example, if the front of your house is the lowest point of your yard and the air conditioner is mounted to a window on the side of the house, place the hose so the end faces the front of your home.
Cut the hose 1 foot past the corner of the house. Cutting the hose at this location ensures that the water condensing from the air conditioner extends past the home and will not drain into the ground directly next to your foundation.