Proper sizing of the bike needs to occur before use to prevent injury and to encourage both efficiency and comfort. With one pedal lowered mount the bike and make sure that you can place your heel on the pedal with your knee slightly bent. Change the seat as needed, but make sure to step off the machine before adjusting the seat and to firmly screw in or set the seat prior to mounting it again.
Many types of bikes exist. They are great for measuring progress or output by way of distance traveled, wattage or calories.