The Padron is the equivalent to the electoral roll in the UK, although does not give foreigners full voting rights. Foreigners can register to vote in local elections although are not permitted to vote in national elections. Unless they become a full Spanish citizen.
It is important for a local government to have all its residents registered on the Padron as they are allocated regional and national budgets, based on the number of residents in a town. It can be the difference between having a fire station, road investment and community swimming pool.
You will be asked to produce a Padron for many administrative tasks and purchases. Basically, it is a proof of address. You will need one to buy a car, change your driving licence, register for health care etc.
It is relatively easy to obtain a Padron in the office of the council in the Old Town of Javea. There is an English speaking helpdesk, although you only need a few words and the relevant paper work- which are your NIE or Residencia, passport, a rental contract or your property deeds.