Look on the side wall of the tire. It will give you the size and the recommended air pressure range (min/max), might even have directional arrows depending on the tread pattern.

You'll want to get a floor pump that has a gauge. Use the floor pump to 'top off' at regular intervals (based upon tire width and pressure- narrow, high pressure tires need to be topped off more often than wide, low pressure tires), as trying to maintain pressure with a mini pump gets to be old fast.