internal power filters consist of a pump with a filter cartridge underneath, often they will have a venturi feacture allowing them to blow air into the aquarium as well as returning clean water. They have an impellor as a moving part which can be replaced as necessary and are available seperately.
When cleaning out any internal power filter it is important that the sponge is cleaned out in water from the aquarium. Simply get a jug of aqaurium water and squeeze the sponge out until it becomes clean and replace sponge- never wash out under thte tap as this will kill off any benefial bacteria within the sponge. Then top up the aquarium water with water treated with dechlorinator.