This is your Neutral/Drive pedal. When you are vacuuming or using the carpet shampooer in the upright position, push down the Drive (D) pedal. This activates Tech Drive power assist to make pushing your Kirby easy.
For the balance of product usage (i.e. cleaning hard floor surfaces, vacuuming in canister mode with attachment hose, vacuuming in hand held mode, using air pump, turbo accessory, etc.) push down the Neutral (N) pedal.