The digital signal is transmitted by geostationary satellites: for receiving it, you need to install a satellite dish. You can install it on a wall, balcony, or roof.
Instead of installing an 'ugly' dish, we also have aesthetical solutions like the DigiGlobe, or the DigiFlat...
Then we will run a 'cable' between the Digital LNB and the Digital Box.
The Digital Box or Decoder transfers the binary data coming from the Dish to pictures and sounds on your screen.It can receive the free channels means, without smart card.
Or receive and decode a scrambling signal, means with a smart card.