What is the correct height for your bike seat? You should get almost full extension of your legs at the bottom of the pedaling stroke. Although you normally center the ball of your foot over the axis of the pedal while riding, you can test for proper seat height by leaning against a wall, placing your heels on the pedals, and pedaling slowly backward. Your legs should be just fully extended when your heels are on the pedals.
If it has been a long while since you have ridden and you are somewhat concerned, it is quite OK to set the seat as low as it will go until you are confident again.