When you buy a brand new car, depending on the make/model/derivative, you will generally be given the On The Road price. Most customers at dealers will use this as a starting price and barter the price down to do a deal.
The P11d value price is the official list price of the vehicle, it will usually include the vehicle price and any additional options, these can include: Special Paints, Sat Nav Upgrades, etc. HMRC use the P11d value along with the CO2 emissions to set your Company Car Tax or Benefit in Kind (BIK).