You take the pill daily. Because of the hormones that are in the pill, your egg does not ripen. You therefore cannot conceive. You take the pill for three weeks. Then you have a stop week and a period. If you stop taking the pill, you can soon become pregnant again.
Advantage: You can postpone your period by skipping your stop week.
Disadvantage: You have to remember it every day. If you forget to take it, you can become pregnant.