Hornby and Bachmann both have sets to get you started, they range in price but generally have the same track in them, they include controllers.
There are two types though. One is just a basic set, with a standard (DC) controller and a standard (DC) train. The other is known as DCC starter sets, these differ slightly from the standard sets in having a basic DCC controller and a DCC fitted train. A basic DCC controller is fine for small layouts, but as the layout gets bigger and you get more trains you may require a better controller.
A search on google may bring up many topics on DCC, or even a quick look at the Hornby or Bachmann websites, but basically it is a more advanced way of controlling trains, using a 'decoder' in the locomotive. DC trains should not be used on DCC layouts, however DCC Locomotives can be used on DC layouts.
Some DC locomotives are able to be converted to DCC very easily, with a factory fitted socket inside the locomotive, these are usually refered to as DCC Ready or DCC Friendly, but are otherwise just DC locomotives. Virtually any DC locomotive can be made into a DCC locomotive.
Designing a layout can be done using computer software like Anyrail or Hornby Virtual Railway, or by getting Hornby track symbols from your local model shop.
Without wishing to steer you away from this forum (which can be very useful for real railways), there are other sites which are better suited to asking questions about model railways.
http://www.newrailwaymodellers.co.uk
http://www.rmweb.co.uk