W salam. Congratulations on the new purchase. It is a beautiful ride.
Bro I've bought a 2013 Nissan Moco S myself this month. The S button is for driving downhill on a slope. What it does is allow you better control and braking ability so your car doesn't pick up too much speed as it would in normal acceleration mode. So press S when driving downhill or a downward slope. make sure that your display shows the "S" mode when you press the S button. when you want to go back to normal mode just press the S button on your gear again.