Freeview is a terrestrial service. If you've got a reasonably good quality aerial (with good quality cabling) you probably need to do nothing more than buy a Freeview box (for around £15 to £20, from any big supermarket or Argos) and plug it in, between your existing aerial and your TV. (That assumes that your TV has got a Scart socket. Unless it's really old it almost certainly has. If it hasn't, post again for information regarding your options). Getting it set up is dead easy; the instructions will tell you how to get it to tune in all of the stations automatically, just by pushing a couple of buttons.
The alternative to Freeview is Freesat, which (as the name implies) is a satellite-based service, and so requires a dish. Since it would work out far more expensive for you to install, just stick to Freeview.
Chris