Tire gauges are available in every discount store for very little money. Every driver should have one in the glove compartment. Even the cheap ones are usually accurate to within a pound or two.
Checking the oil, tire pressure and water levels are three things every beginning driver should learn to do before ever getting behind the wheel. My sister was nearly 50 before she learned to do these things herself.
Checking the tire pressure takes about two minutes, and can be done any time. It's always a good idea to check the tire pressure about once every couple of weeks, and certainly before taking the vehicle on a long trip. Keeping the tires properly inflated can save on gas mileage in the long run.