What position should overdrive button be in on a Nissan sunny automatic car wheh driving it?

In Nissan Sunny (and some other cars too), overdrive is ON when the button is DEPRESSED and there's NO LIGHT in the dashboard. The automatic transmission will utilise all the 4 forward gears (the 4th gear being the overdrive that helps in fuel economy -- similar to 5th gear in a manual gearbox). This is the recommended setting for normal driving.

When the button is NOT DEPRESSED, you turn OFF overdrive, and the indicator LIGHTS UP in the dashboard. In this mode, the automatic transmission will NOT shift into 4th gear.