The verb advertise means to publicize a service or product in order to try to get you to buy or use it. If you see people eating delicious-looking chocolate in a television commercial, for example, you'll probably want to buy it.
You don't have to use television, radio, or print media to advertise something — or even try to sell it at all. In fact, the word advertise can also simply mean to call attention to something. Your neighbors might advertise their lottery win by parking flashy cars in the driveway and having an endless supply of packages delivered to their house.