If you've only got one TV you only need a 1-way booster:
http://www.amazon.co....id=1267573147&sr=1-11
or
http://www.amazon.co....id=1267573147&sr=1-15
(My preference would be for the one in the second link there. It's got a maximum gain of 20db - which is reasonably high - whereas there's no gain figure stated for the first one).
You simply plug the unit into any convenient power socket and then plug your aerial into the 'input'. You'll also need a 'fly lead' (which is just a short length of aerial cable with a plug at either end) to connect between the unit's output and your TV. Almost every 'pound' shop in the country (and most branches of Tesco) sell them, as does Amazon:
http://www.amazon.co....qid=1267573730&sr=1-1
If you'd rather buy a signal booster on the High Street, try Tesco Extra or Asda. (Maplin Electronics sell them but they charge £14.99).
Chris