For easy reference, the recommended tire pressure is always printed on the sidewall of your tire. Look on your tire's sidewall for tire pressure recommendations for your folding bike model.
Make sure to maintain the recommend tire pressure. Do not exceed the maximum tire pressure listed.
Make sure to check your tire pressure before every ride. Poorly inflated tires are much more likely to suffer a puncture caused by the inner-tube being pinched by the rim.
Low tire pressure can also cause excessive wear on the tread and sidewall of the tire, where the tire is least protected. Over time, this can lead to premature tire wear. An underinflated tire also greatly increases the "rolling resistance," requiring more pedaling effort.
Maintaining proper tire pressure will make for a more enjoyable, efficient ride and extend the life of your tires.
CAUTION: A gas station hose may inflate a bicycle tire too rapidly, and the pressure indicated is often inaccurate. Excessive pressure can cause the tire to explode or fail. Use a hand-operated pump with an appropriate gauge.