That little button is the power button. It changes the way the transmission shifts gears. It pretty much raises the shift points so that they are closer to the redline. It will perform like a manual if you turn the Overdrive off and flip the switch to Power mode. It will shift high and give you more torque. But it sucks down gas quicker too.
N = Normal
A/T= just the name of the button cause you can't put it on there. Auto Trans
P= Power
