Your pond will need an electric supply to power the equipment essential to running it. This equipment may consist of filter pump, UV clarifier, air pump, heater and perhaps lights as well. You may not want all of this to begin with but it is wise to consider it from the outset. Pond electrics are easy to overlook when planning your pond but it will be much easier and neater if you can incorporate them into your initial design.
It is often best to have a switch box to distribute power to all of your separate pieces of equipment and these come with various numbers of outlets to suit what you decide you need.
These switch boxes consist of a mains feed into them and 3, 4, 5 or more separate, switched outlets which are individually fused.
Saftey around water is paramount so the mains feed in must have RCD circuit breaker protection in case of mishap.