To postpone something is to put it off until later. You can postpone an appointment today and reschedule it for tomorrow.
Anything you're putting for is being postponed: people postpone things they don't have time to do or just don't want to do. Since doctor and dental appointments are no fun, people postpone them a lot. You can postpone small things, like going to the store or watching a video. The government can postpone big things, like the passing of bills or the invasion of another country. People who procrastinate are constantly postponing. When you see the word postpone, think "Later!"