Currently TV is sent to your house as an analogue signal and you can pick up 5 channels via your aerial (BBC, BBC2, ITV, Ch4, Ch5)
Gradually, and more so in the future, TV will be sent to the aerial in your house as a digital signal, and you can get more than 5 channels.
Over the next few years the analogue signal will be turned off and ONLY the digital signal will be available.
Because most TVs can currently only accept analogue you need a special box (a freeview box) to pick up the digital signal and convert it to analogue so it can be displayed on your TV.
Once the analogue signal is switched off ONLY the digital signal will be available.
So if you have ANY analogue TVs they would need a freeview box so you can watch TV (this applies to ALL TVs, such as portables, ones in your bedroom or caravan and so on).
If you have a VHS video with an analogue tuner in it then it will not work as their will be no analogue signal (when you record on your VHS you are often recording from the TV tuner inside the VHS).
Many modern TVs already have a freeview box built in (IDTV) so they are already setup to get the digital signal.
This does NOT apply to Sky or cable TV whiich is already digital (and does not come thorugh your aerial anyway)
Ask again if there is anything you do not understand.
More here
http://www.digitaltelevision.gov.uk/